Space
Solar system; Formation, planets, wonders and everything you need to know
Solar system; Formation, planets, wonders and everything you need to know
The solar system is one of the billions of star systems in the Milky Way galaxy, which consists of the average central star of the Sun. The order of placement of the planets in this system from the nearest mass to the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and possibly the ninth planet.
The solar system starts from the sun continues to the Kuiper belt and finally reaches the boundary of the Heliopass. According to scientists, the edge of the solar system is approximately 15 billion kilometers away from the sun. On the other side of the Heliopass, there is a huge oval-shaped cloud called the Oort cloud, which surrounds our solar system.
Table of Contents
- What is the solar system?
- The origin of the solar system
- Size and distance in the solar system
- Sun
- The planets of the solar system
- What is a planet?
- Mercury
- Venus
- planet Earth
- planet mars
- Jupiter
- Saturn
- Uranus
- The planet Neptune
- asteroid belt
- Kuiper belt
- Pluto
- The ninth planet
- edge of the solar system
- The largest planets in the solar system
- Discoveries and travels of the solar system
- Photos of the solar system
- Conclusion
What is the solar system?
The solar system is a collection of planets, moons, asteroids, comets, and gas and dust that revolve around the Sun star. This system consists of rocky planets including Mercury, Venus, Earth, and Mars, gas giants including Jupiter and Saturn, and ice giants including Uranus and Neptune.
Between Mars and Jupiter, there is a set of asteroids known as the Asteroid Belt, and on the other side of Neptune, a set of small icy bodies known as the Kuiper Belt revolve around the Sun. Objects such as the dwarf planet Pluto are also considered part of the Kuiper belt.
The origin of the solar system
About 4.6 billion years ago, a dark cloud of gas and dust underwent a gravitational collapse. This cloud compressed and turned into a rotating disk known as the solar nebula. The heat and pressure were eventually so great that the hydrogen atoms fused together to form helium. Nuclear interactions released large amounts of energy and the Sun was formed.
The Sun collected approximately 99% of the material in the solar nebula, and the rest of the material formed similar clumps inside the rotating disk. Some of these materials reached enough mass and gravity to form globular masses or planets, dwarf planets, and moons. The remaining fragments formed meteorites, comets, and other moons that make up the solar system.
Meteorites, or celestial rocks that fell to Earth, helped scientists estimate the age of the solar system. Some of these small fragments originated from moons or planets that can provide fascinating scientific information about the chemical properties and history of their parent matter. Some others were circulating in the solar system from the very beginning and before the formation of planets. The Allende meteorite, which fell to Earth in 1969, is the best-known meteorite with an age of 4.55 billion years.
According to scientists, the solar system was created during the explosion of a nearby star or the supernova process . According to this theory, the explosion caused shock waves to be sent into space and these waves compressed the solar nebula and finally led to its collapse. The supernova likely drove material into the nebula.
The stages of the formation of the solar system
Size and distance in the solar system
The solar system is so big that it is almost impossible to imagine its size using units like kilometers. The distance from the Earth to the Sun is approximately 150 million kilometers, but the distance from the Sun to the farthest planet in the solar system, Neptune, is 4.5 billion kilometers. Now compare this distance with the average distance that a healthy person can walk non-stop in one day (32 km) or the distance to the International Space Station (400 km).
The best way to estimate the size of the solar system is to create a scale model that shows the distance of the planets from the sun. Astronomers use the distance between the Earth and the Sun (150 million kilometers) as a unit of measurement known as the astronomical unit. Therefore, 150 million kilometers is equal to one astronomical unit, or AU for short.
Thus, the distance between Mercury and the Sun (0.43 AU), Venus is 0.7 AU, Earth is 1 AU and Mars is 1.5 AU. Then we reach the asteroid belt, which is 2.8 AU away from the Sun. The gas giants Jupiter and Saturn are 5.2 and 9.5 AU from the Sun, respectively, and the ice giants Uranus and Neptune are 19.8 and 30 AU, respectively.
The Kuiper Belt is 50 AU away from the Sun and finally, the border of the Solar System or Heliopass is 123 AU away from the Sun.
Read More: The International Space Station
Sun
An artist’s rendering of the Parker probe exploring the Sun
The sun is at the center of the solar system and constitutes approximately 99.8% of the mass of its system. The sun provides the necessary energy for life on Earth. This composite yellow dwarf star consists of 91% hydrogen and 8.9% helium. The Sun is relatively small compared to other stars and is one of hundreds of billions of stars in the Milky Way galaxy.
The planets of the solar system
The four inner planets of the solar system, Mercury, Venus, Earth, and Mars, are classified as terrestrial planets or rocky worlds due to their rocky surface.
The four outer worlds of the solar system, namely Jupiter, Saturn, Uranus, and Neptune, are called Jupiter-like planets due to their larger size than the rocky planets. Most of these planets are made up of gases such as hydrogen and helium, although some planetologists believe that some of these planets have solid cores.
The planets Jupiter and Saturn are called gas giants, while Uranus and Neptune, the two outermost worlds of the solar system, are classified as ice giants because they are composed of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur, and have a thick mantle. They have methane, ammonia, and frozen water.
What is a planet?But before introducing the planets of the solar system, it is necessary to get acquainted with the definition of a planet. According to the standard definition, a planet is a mass of sufficient size that revolves around the Sun and itself. But it is not big enough to undergo nuclear fusion like a star. It has also cleared its vicinity of a large number of other objects.
The exact definition mentioned above shows what should be included in the category of planets and what should not be included in this group. However, the problem arose when astronomers discovered a large number of planet-like bodies in the solar system. For example, Pluto was one of the objects that could not meet all the above conditions and was classified as a dwarf planet.
Most of the gaseous planets are composed of hydrogen and helium and probably have a solid core; While the core of rocky planets is often molten.
Pluto’s problem is its small size and strange orbit that cannot clear nearby objects. It also has a lot in common with the Kuiper belt. According to the IAU definition, this planet and other small globular worlds including Eris, Haumea and Makimaki, other Kuiper belt objects are classified as dwarf planets.
Ceres is another globular body in the asteroid belt between Mars and Jupiter, which belongs to the group of dwarf planets. Ceres was classified as a planet when it was first discovered in 1801 but was later recognized as an asteroid. However, this definition was not enough because it was much larger and more spherical than asteroids. Therefore, astronomers classified this object as a dwarf planet in 2006.
Mercury
Mercury is the closest planet to the Sun from the perspective of NASA’s Messenger probe.
- Discovery: It was known to the ancient Greeks and can be seen in the sky with the naked eye.
- Naming: Mercury, derived from the name of the messenger god in Roman mythology
- Diameter: 4878 km
- Year: 88 Earth days
- Day: 58.6 Earth days
- Number of moons: zero
Mercury is the closest world to the sun and the smallest planet in the solar system. This planet is only slightly larger than the Earth’s moon and completes its orbit around the sun in 88 days.
The temperature difference between the day and night of Mercury is significant. The temperature of Mercury during the day reaches 450 degrees Celsius, which is enough to melt lead. During the night, the temperature drops to minus 180 degrees Celsius. Mercury’s atmosphere is very thin and contains elements such as oxygen, sodium, hydrogen, helium, and potassium. Since this weak atmosphere cannot prevent meteorite collisions, Mercury’s surface is full of impact craters, just like Earth’s moon.
During its five-year mission, NASA’s MESSENGER probe made interesting findings about Mercury that defied astronomers’ expectations. One of these findings was the discovery of water ice and frozen biological compounds in the north pole of Mercury, as well as the significant role of volcanic activity in the formation of the planet’s surface.
Venus
This image of Venus was captured in 2020 by NASA’s Mariner 10 probe.
- Discovery: It was known to the ancient Greeks and can be seen with the naked eye.
- Naming: Venus, derived from the name of the goddess of love and beauty in Roman mythology
- Diameter: 12,104 km
- Year: 225 Earth days
- Day: 241 Earth days
- Number of moons: zero
Venus is the second planet from the sun and the hottest planet in the solar system. The thick atmosphere of Venus is composed of compounds such as sulfuric acid clouds. Venus can be considered as one of the clear examples of the greenhouse effect.
The average surface temperature of Venus reaches 465 degrees Celsius and its surface pressure is 92 bar (9200 kilopascals), which can disintegrate a human being. Strangest of all, Venus rotates slowly and rotates against the direction of other planets, i.e. from east to west.
Venus is sometimes called Earth’s twin because the planet is close in size to Earth and, based on radar images, has numerous mountains and volcanoes. But in reality, Earth and Venus have many differences from each other.
Since Venus is the brightest object in the night sky after the moon, the Greeks thought that they were two different objects; Hesperus as a night star and Eospherus as a morning star. This very brightness is why Venus is sometimes mistaken for a UFO.
planet Earth
One of the most accurate pictures of the Earth. This composite image is the result of images recorded by the Processing Infrared/Visible Image Radiometer (VIIRS) of the Suomi NPP satellite.
- Name: Earth is derived from the German word “Die Erde” which means earth.
- Diameter: 12,760 km
- Year: 365.24 days
- Day: 23 hours and 56 minutes
- Number of moons: 1
Earth, our home, is the third planet from the Sun. Earth is a blue world with two-thirds of it covered by water. Earth’s atmosphere is rich in nitrogen and oxygen, making it the only life-friendly world we know.
The earth rotates at a speed of 467 meters per second. But this speed is slightly higher in the equator. The speed of the earth’s rotation around the sun reaches 29 km/s. Earth is also the largest rocky planet in the solar system and has one moon. According to scientists, an object hit the earth early in its formation and a piece of it was thrown into the sky and thus the moon was formed.
planet Mars
A mosaic image of the Vals Marineris hemisphere of Mars. This image is the result of combining 102 Viking orbiter images.
- Discovery: It was known to the ancient Greeks and can be seen with the naked eye.
- Name: Mars, derived from the name of the god of war in Roman mythology
- Diameter: 6787 km
- Year: 687 Earth days
- Day: 24 hours and 37 minutes
- Number of moons: 2
Mars is the fourth planet from the Sun. This desert-like and cold planet is covered with iron oxide dust and therefore appears red. Mars has similarities with Earth. It is primarily rocky like Earth, has mountains and valleys, and has a storm system like Earth’s, ranging from small tornado-like ovens to dust storms that cover the entire planet.
Scientific evidence shows that Mars was a warmer and wetter world billions of years ago, and probably had rivers and maybe oceans flowing in it. Although the Martian atmosphere is too thin for surface liquid water to flow, wetter Martian remnants exist today. Martian ice sheets the size of the state of California are located under the surface of Mars, and on the other hand, both poles of Mars have water ice covers.
According to scientists, ancient Mars had the necessary conditions to support life such as bacteria and other microbes. They hope to find signs of this past life and possibly present life forms. This hypothesis became the basis for launching several missions to Mars; So that today the red planet is one of the most familiar and most explored objects in the solar system.
Jupiter
An extraordinary image of Jupiter captured by the Hubble Space Telescope on August 25, 2020.
- Discovery: It was known to the ancient Greeks and can be seen with the naked eye.
- Naming: Jupiter, derived from the name of the god of gods in Roman mythology
- Diameter: 139,822 km
- Year: 11.9 Earth years
- Day: 9.8 Earth hours
- Number of moons: 95
Jupiter is the fifth planet from the sun and the largest planet in the solar system. This gas giant has twice the mass of all other planets in the solar system.
Jupiter’s swirling clouds are colorful due to the combination of a variety of materials such as ammonia ice, ammonium hydrosulfide crystals, and water ice and vapor. One of Jupiter’s most famous features in its swirling clouds is the Great Red Spot, which is more than 16,000 kilometers in diameter and is so large that it can swallow almost three Earths.
Jupiter also has the strongest magnetic field and 95 moons, the most famous of which are Ganymede, Io, Callisto, and Europa, also known as the Galilean moons.
Saturn
The Hubble Space Telescope captured this image of Saturn during the Northern Hemisphere summer on July 4, 2020.
- Discovery: It was known to the ancient Greeks and can be seen in the night sky with the naked eye.
- Naming: Saturn, derived from the name of the god of agriculture in Roman mythology
- Diameter: 120,500 km
- Year: 29.5 Earth years
- Day: approximately 10.5 hours by land
- Number of moons: 145 moons
Saturn, the sixth planet from the Sun, is famous for its huge and bright ring system. Although Saturn is not the only ringed planet in the solar system. When Galileo first studied Saturn in the early 1600s, he thought it was a three-part mass: a planet and two large moons on either side. He didn’t know he was seeing a ringed planet. More than 40 years later, Christian Huygens proved the existence of Saturn’s rings.
Like Jupiter, Saturn is a gas giant and the least dense planet in the solar system. This planet also has a large number of moons, according to the latest statistics, their number reaches 145. With this number of moons, Saturn is considered the king of the solar system’s moons. Enceladus is one of Saturn’s moons covered with an icy ocean, which astronomers say could be a promising target for extraterrestrial life.
Saturn’s rings are composed mostly of ice and rock, and scientists are still unsure how they formed.
Uranus
Image of Uranus captured by NASA’s Chandra X-ray Observatory.
- Discovery: 1781 by William Herschel (before this date people thought Uranus was a star).
- Naming: the embodiment of heaven and the name of one of the gods in Greek mythology
- Diameter: 51,120 km
- Year: 84 Earth years
- Day: 18 hours on land
- Number of moons: 27
The planet Uranus, the seventh planet from the sun, has strange and unique features. The clouds of Uranus are composed of hydrogen sulfide, which is the same chemical that causes eggs to rot and smell bad. In the second degree, like Venus, Uranus rotates from east to west, but unlike Venus or any other planet, its equator is perpendicular to its orbit and it can be said to rotate sideways.
According to astronomers, a mass twice the size of Earth collided with Uranus about 4 billion years ago and caused Uranus’ extreme axial deviation. This deviation leads to marginal seasons with a duration of at least 20 years, so that sunlight shines on one pole of Uranus for 84 years.
It seems that the said collision transferred some of the rock and ice of Uranus into its orbit and these rocks and ice later formed the moons of Uranus. Methane in the atmosphere of Uranus is the main reason for its blue-green color. Uranus has 13 sets of rings.
The planet Uranus also holds the record for the coldest temperature recorded in the solar system, minus 224.2 degrees Celsius. The average temperature of Uranus reaches minus 195 degrees Celsius.
The planet Neptune
Neptune is the planet with the fastest winds in the solar system.
- Discovery: 1846
- Naming: Neptune, derived from the name of the god of water and sea in Roman mythology
- Diameter: 49,530 km
- Year: 165 Earth years
- Day: 19 hours on land
- Number of moons: 14
Neptune is the eighth and farthest planet from the Sun. The average temperature of Neptune in the upper part of the clouds reaches minus 210 degrees Celsius. This planet is about the same size as Uranus and is known for its strong supersonic winds.
Neptune was the first planet to be discovered using mathematics. German astronomer Johann Galle used mathematical calculations to find Neptune with a telescope.
Neptune is about 17 times heavier than Earth and has a rocky core. The main composition of Neptune is water, methane, and ammonia, which surround this rocky core. The speed of Neptune’s winds reaches 2000 km/h. This planet also has 14 moons.
asteroid belt
The asteroid belt is located between Mars and Jupiter. According to NASA estimates, there are between 1.1 and 1.9 million asteroids in the main asteroid belt that are larger than one kilometer in diameter. The dwarf planet Ceres with a diameter of approximately 950 km is located in this part of the solar system. Several asteroids have orbits that occasionally collide with Earth and other inner planets.
Kuiper belt
Astronomers have long suspected the existence of a band of icy material known as the Kuiper Belt, which lies beyond the orbit of Neptune at a distance of 30 to 55 times the distance from the Earth to the Sun. Since the 20th century, more than a thousand crimes have been discovered in this belt. According to scientists’ estimates, the Kuiper Belt probably hosts hundreds of thousands of icy bodies larger than 100 km, as well as almost a trillion comets.
Pluto, which today belongs to the group of dwarf planets, is located in the Kuiper belt. Of course, Pluto is not the only one, and Makimaki, Haumea, Eris, and Quavar are among the other known non-Neptunian objects from the group of dwarf planets. Aracut (Altima Tully) is also a binary asteroid located in the Kuiper Belt that was visited by the New Horizons probe in 2019.
Pluto
A panoramic view of the dwarf planet Pluto
- Discovered: 1930 by Clyde Tamba
- Naming: Pluto or Pluton derived from the name of the god of the underworld in Roman mythology
- Diameter: 2301 km
- Year: 248 Earth years
- Day: 6.4 Earth days
- Number of moons: 5
The dwarf planet Pluto was once considered the ninth planet, but since 2006 it has been classified as a dwarf planet. The reason for this problem was the non-compliance with the existing criteria in the definition of the planet. According to the definition of the International Astronomical Union, a planet is a celestial body that firstly orbits the Sun, secondly has enough gravity to become a spherical or almost spherical body, and thirdly clears the vicinity of its orbit. be Pluto did not fit the third criterion of logic and therefore was removed from the group of planets.
Pluto has a highly elliptical orbit so it sometimes even interferes with Neptune’s orbit. On the other hand, Pluto’s orbit is not in the same plane as other planets, but it revolves around the Sun at an angle of 17.1 degrees above or below them.
Because of this strange orbit, Pluto was considered the eighth planet from the Sun from 1979 to early 1999, but on February 11, 1999, when it crossed the path of Neptune, it again became the most distant planet in the Solar System, until it was officially removed from the Sun in 2006. The group of planets is out.
Smaller than Earth’s moon, Pluto is a cold, rocky world with a thin atmosphere. On July 14, 2015, the New Horizons probe performed several low-altitude flybys around Pluto, presenting a new view of the dwarf planet to the scientific world that defied many expectations.
Pluto is actually a very active ice world, covered in glaciers, ice mountains, icebergs, and possibly even glaciers that spew ice made of water, methane, or ammonia.
The ninth planet
According to estimates, the hypothetical ninth planet has approximately 10 times the mass of Earth.
In 2016, researchers raised the possibility of the ninth planet . This object, also known as Planet X, is estimated to have 10 times the mass of Earth and orbits the star of our system at a distance between 300 and 1,000 times the distance between Earth and the Sun. In fact, this planet’s year may last between 10,000 and 20,000 Earth years. Scientists have not been able to observe the ninth planet so far and have guessed its existence based on its gravitational effects on other objects in the Kuiper belt.
According to some hypotheses, the hypothetical ninth planet could be a primordial black hole that formed shortly after the Big Bang and was trapped by the solar system. Unlike black holes that result from the collapse of massive stars, primordial black holes were formed by gravitational perturbations less than a second after the Big Bang and may be very small (as little as five centimeters in diameter), making them difficult to detect.
Astronomers have not yet reached a clear conclusion regarding the ninth planet. Based on a 2022 survey by the ACT telescope in Chile, there are thousands of candidate sources for the planet, but none have yet been confirmed.
Edge of the solar system
The heliosphere surrounds the solar system like a bubble and its boundary is called the heliopass.
By passing through the Kuiper belt, we reach the edge of the solar system or the Heliopass. The heliosphere is a vast, tear-shaped region of space with a large amount of charged particles received from the sun. According to many astronomers, the boundary of the heliosphere, which is called the heliopass, is approximately 15 billion kilometers from the sun.
The Oort cloud is located after the Kuiper belt at a distance of 2,000 to 2,500 AU from the Sun, and the distance of its outer edge from the Sun is estimated to be between 10,000 and 100,000 AU. As mentioned in the previous sections, one astronomical unit is approximately equal to 150 million kilometers. The Everett Cloud is home to billions or perhaps trillions of particles.
The largest planets in the solar system
Jupiter compared to other planets
Jupiter is by far the largest planet in the solar system, so if you add the mass of all the planets in the solar system together, Jupiter will still be two and a half times more. Compared to Earth, Jupiter is 318 times the size of Earth. The radius of this planet reaches 69,911 km or one-tenth of the sun. Saturn is the second largest planet in the solar system. Saturn has 95 times the mass of Earth; however, it is the least dense planet in the solar system, so that it can float on water.
Discoveries and travels of the solar system
According to NASA, more than 254 probes have left Earth’s orbit so far. A large part of these spacecrafts and probes were dedicated to the exploration of the solar system.
Parker probe is the only spacecraft that managed to reach the closest distance to the Sun and will break this record in the coming years. The probe will release information about the solar radiation, surface, corona, and solar wind.
Famous probes such as NASA’s MESSENGER, Mariner 10, and Beppy Columbo have visited Mercury and revealed valuable information such as the discovery of water ice and the thin atmosphere of Mercury.
In general, 46 probes have visited Venus so far, the most successful of which are the Venus Express, Mariner 10, and Magellan missions. These probes released information about the atmosphere of Venus and its possible volcanic activity.
There are many satellites in the earth’s orbit whose task is to check weather and atmospheric conditions. Also, the International Space Station is the largest man-made structure in space, and astronauts are engaged in research work there.
In the last 60 years, six lunar landers have landed on the surface of the moon, the first of which was the Apollo 11 mission. Also, in recent years, orbiters were placed in the orbit of the moon, whose most important achievement was finding water ice around the poles of the moon. Space agencies aim to land on the surface of the Moon again in the coming years and use the Earth’s moon as a research base.
Apollo 11, the first human landing on another world.
Mars is the most explored planet in the solar system, which has been assigned more than 50 exploration missions. The most famous Mars missions include the Curiosity rover, Perseverance, and the MRO orbiter. Each of the Mars rovers and probes is investigating a certain area and so far they have published important and valuable data such as the discovery of water ice, polar ice cover, and methane on Mars. In the not-too-distant future, human explorations will be added to this collection.
Among the outer planets of the solar system, Jupiter and Saturn are two of the most explored examples. So far, eight spacecraft have been sent specifically to visit Jupiter, and two other probes have performed low-altitude flybys of the planet. The Juno probe is still in Jupiter’s orbit and has provided valuable information about Jupiter’s atmosphere and its important moons.
Voyager 2, is the first and so far the only probe to visit the planets Uranus and Neptune.
Cassini is the most famous probe that visited Saturn, and in addition to recording beautiful images of Saturn and sending information about its atmospheric conditions and rings, it investigated two important moons of Saturn, Titan and Enceladus. Two of Cassini’s most important discoveries in visiting these moons were the discovery of methane lakes on Titan and glaciers and ice oceans on Enceladus.
The two famous probes Voyager 1 and 2 successfully visited the outer planets of the outer solar system, including Jupiter, Saturn, Uranus, and Neptune. Voyager 2 is the only probe that visited Uranus and Neptune up close.
New Horizons is the only probe to visit the dwarf planet Pluto, sending back important information about surface conditions, moons, and other Kuiper Belt objects.
In addition to the probes that visited the planets of the solar system, a series of missions were dedicated to the study of objects in the asteroid belt. Also, the Hubble and James Webb telescopes have sent important images and data from the solar system.
Conclusion
The solar system is a collection of planets, moons, asteroids, and comets around the sun. The planets of the solar system are divided into two groups: rocky and gaseous planets. Earth is a rocky planet and the only planet known to host life in the entire universe. So far, many probes have been sent to different planets of the solar system. Meanwhile, Mars is considered the most explored and familiar planet of the solar system, which mankind has made the most efforts to investigate. Today, humans are carrying out missions and building new probes to investigate the potential of life on the planets and moons of the solar system, and in this way, they will get help from ground and space telescopes.
How the James Webb Space Telescope deepens cosmology’s biggest controversy
Summary of the article:
- Almost a century ago, Edwin Hubble discovered the expansion of the universe and calculated the expansion rate or the cosmic constant.
- Since Hubble, many groups have tried to measure the expansion rate of the universe. However, the values they obtained differed from the theoretical predictions. This difference is called Hubble tension.
- Scientists today use three methods to measure the expansion rate of the universe: Cephasian variable stars, TRGB red giant stars, and JAGB asymptotic giants.
- However, the Hubble tension still exists, indicating that the methods for calculating the Hubble constant suffer from a systematic flaw.
- Researchers hope to be able to use the James Webb telescope in the coming years to achieve more accurate measurements of the universe’s expansion rate and thus resolve the Hubble tension.
Almost a century ago, Edwin Hubble discovered that the universe was getting bigger. However, today’s measurements of how fast the universe is expanding are contradictory. These discrepancies show that our understanding of the laws of physics may be incomplete. On the other hand, everyone expected the sharp eyes of the James Webb telescope to bring us closer to the answer to the riddle; But a new analysis of the telescope’s long-awaited observations once again reflects inconsistent expansion rates from different types of data, while pointing to possible sources of error.
Two competing groups have led efforts to measure the rate of expansion of the universe, known as Hubble’s constant, or H0. A group led by Adam Reiss of Johns Hopkins University, relying on the known constituents of the universe and the governing equations, has consistently calculated the Hubble constant to be approximately 8 percent higher than the theory predicts the universe’s expansion rate. This discrepancy, known as the Hubble tension, indicates that the model of the cosmological theory may have missed some elements such as raw materials or effects that speed up the expansion of the universe. Such an element can be a clue to a more complete understanding of the world.
This spring, Reiss and his team published new measurements of the Hubble constant based on data from the James Webb Telescope and found a value consistent with their previous estimates. However, a rival group led by Wendy Friedman of the University of Chicago warns that more precise measurements are needed. The team’s measurements of the Hubble constant are closer to the theoretical estimate than Riess’ calculations, suggesting that the Hubble stress may not be real.
Since the commissioning of the James Webb Telescope in 2022, the astrophysical community has been waiting for Friedman’s multidimensional analysis based on telescope observations of three types of stars. The results are now as follows: the two-star types provide estimates of the Hubble constant that are in line with the theoretical prediction; While the results of the third star, which is the same type used by Reiss, are consistent with his team’s higher estimates of Hubble’s constant. According to Friedman, the fact that the results of the three methods are contradictory does not mean that there are unknown physical foundations, but that there are some systematic errors in the calculation methods.
Contradictory world
The difficult part of measuring cosmic expansion is measuring the distance of space objects. In 1912, American astronomer Henrietta Levitt first used pulsating stars known as Cephasian variables to calculate distances. These stars flicker at a rate proportional to their intrinsic luminosity. By understanding the luminosity or radiant power of a Cephasian variable, we can compare it with its apparent brightness or dimming to estimate its galaxy’s distance from us.
Edwin Hubble used Levitt’s method to measure the distances to a set of galaxies hosting the Cephasian variable, and in 1929 he noticed that the galaxies that are farther away from us are moving away faster. This finding meant the expansion of the universe. Hubble calculated the expansion rate to be a constant value of 500 km/s per megaparsec. In other words, two galaxies that are 1 megaparsec or approximately 3.2 million light years apart are moving away from each other at a speed of 500 km/s.
As progress was made in calibrating the relationship between the pulsation frequency of Cepheids and their luminosity, measurements of the Hubble constant improved. However, since the Cephasian variables are very bright, the whole approach used has limitations. Scientists need a new way to measure the distance of galaxies from each other in the infinite space.
In the 1970s, researchers used Cephasian variables to measure the distance to bright supernovae, and in this way they achieved more accurate measurements of the Hubble constant. At that time, as now, two research groups undertook the measurements, and using supernovae and Cephasian variable stars, they achieved contradictory values of 50 km/s per megaparsec and 100 km/s per megaparsec. However, no agreement was reached and everything became completely bipolar.
Edwin Hubble, the American astronomer who discovered the expansion of the universe, stands next to the Schmidt telescope at the Palomar Observatory in this photo from 1949.
The launch of the Hubble Space Telescope in 1990 gave astronomers a new and multi-layered view of the universe. Friedman led a multi-year observing campaign with Hubble, and in 2001 he and his colleagues estimated the expansion rate to be 72 km/s/Mpa with an uncertainty of at most 10%.
A Nobel laureate for the discovery of dark energy, Reiss got into the expansion game a few years later. In 2011, his group found the Hubble constant to be 73 with a three percent uncertainty. Soon after this, cosmologists excelled in another way. In 2013, they used Planck’s observations of light left over from the early universe to determine the exact shape and composition of the early universe.
In the next step, the researchers connected their findings to Einstein’s theory of general relativity and developed a theoretical model to predict the current state of the universe, up to approximately 14 billion years into the future. Based on these calculations, the universe should be expanding at an approximate rate of 67.4 km/s per megaparsec with an uncertainty of less than one percent.
Reese’s team measurement remained at 73, even with the improved accuracy. This higher value indicates that the galaxies today are moving away from each other at a faster rate than theoretically expected. This is how the Hubble tension was born. According to Reiss, today’s Hubble tension shows us that something is missing in the cosmological model.
The missing factor could be the first new element in the universe to be discovered since dark energy. Theorists still have doubts about the identity of this agent. Perhaps this force is some kind of repulsive energy that lasted for a short time in the early universe, or perhaps it is the primordial magnetic fields created during the Big Bang, or perhaps what is being missed is more about ourselves than the universe.
Ways of seeing
Some cosmologists, including Friedman, suspected that unknown errors were to blame for Hubble’s tension. For example, Cephasian variable stars are located in the disks of younger galaxies in regions full of stars, dust, and gas. Even with Hubble’s fine resolution, you don’t see a single Cephasian variable, according to George Afstatio, an astrophysicist at the University of Cambridge. Rather, you see it overlapping with other stars. This density of stars makes measurements of brightness difficult.
When the James Webb Telescope launches in 2021, Reiss and his colleagues will use its powerful infrared camera to peer into the crowded regions that host the Cephasian variables. They wanted to know whether the claims of Friedman and other researchers about the effect of the area’s crowding on the observations were correct.
The 6.5-meter multi-section mirror of the James Webb Space Telescope at NASA’s Goddard Space Flight Center in Maryland. This mirror passed various test stages in 2017.
When the researchers compared the new numbers to distances calculated from Hubble data, they saw a surprising match. The latest results from the James Webb telescope confirmed the Hubble constant measured by the Hubble telescope a few years ago: 73 km/s/Mpa with a difference of one kilometer or so.
Concerned about crowding, Friedman turned to alternative stars that could serve as distance indicators. These stars are found in the outer reaches of galaxies and away from the crowd. One of those stars belongs to the group ” Red Giant Branch ” or TRGB for short. A red giant is an old star with a puffy atmosphere that shines brightly in the red light spectrum. As a red giant ages, it eventually burns helium in its core, and at this point, the star’s temperature and brightness suddenly decrease.
A typical galaxy has many red giants. If you plot the brightness of these stars against their temperature, you reach a point where the brightness drops off. The star population before this brightness drop is a good distance indicator; Because in each galaxy, such a population has a similar distribution of luminosity. By comparing the brightness of these star populations, astronomers can estimate their relative distances.
The Hubble tension shows that the standard model of the cosmos is missing something
Regardless of the method used, physicists must calculate the absolute distance of at least one galaxy as a reference point in order to calibrate the entire scale. Using TRGB as a distance index is more complicated than using Kyphousian variables. MacKinnon and colleagues used nine wavelength filters from the James Webb telescope to understand how brightness relates to their color.
Astronomers are also looking for a new indicator: carbon-rich stars that belong to a group known as the “Jay region asymptotic giant” (JAGB). These stars are far from the bright disk of the galaxy and emit a lot of infrared light. However, it was not possible to observe them at long distances until James Webb’s launch.
Friedman and his team have applied for observation time with the James Webb Space Telescope in order to observe TRGBs and JAGBs, along with more fixed spacing indices and Cephasian variables, in 11 galaxies.
The vanishing solution
On March 13, 2024, Friedman, Lee, and the rest of the team meet in Chicago to find out what they’ve been hiding from each other. Over the past months, they were divided into three groups, each tasked with measuring distances to 11 galaxies using one of three methods: Cephasian variable stars, TRGBs, and JAGBs.
These galaxies also host related types of supernovae, so their distances can calibrate the distances of supernovae in many more distant galaxies. The rate at which galaxies move away from us divided by their distance gives the value of the Hubble constant.
Wendy Friedman at the University of Chicago is trying to fit the James Webb Telescope observations into the Standard Cosmological Model.
Three groups of researchers calculated distance measures with a unique, random counterbalancing value added to the data. During the face-to-face session, they removed those values and compared the results.
All three methods obtained similar distances with three percent uncertainty. Finally, the group calculated three values of Hubble’s constant for each distance index. All values were within the theoretical prediction range of 67.4. Therefore, Hubble’s tension seemed to be resolved. However, they ran into problems with further analysis to write the results.
The JAGB analysis was good, But the other two were wrong. The team found that there were large error bars in the TRGB measurements. They tried to minimize the errors by including more TRGBs; But when they started doing this, they found that the distance to the galaxies was less than they first thought. This change caused the value of Hubble’s constant to increase.
Friedman’s team also discovered an error in Cephaus’s analysis: in almost half of the pulsating stars, the term crowd was applied twice. Correcting this error increased the value of Hubble’s constant significantly. Hubble’s tension was revived.
Finally, after efforts to fix the errors, the researchers’ paper presents three distinct values of Hubble’s constant. The JAGB measurement yielded a result of 67.96 km/s/megaparsec. The TRGB result was equal to 69.85 with similar error margins. Hubble’s constant was obtained at a higher value of 72.05 in the Kyphousian variable method. In this way, different hypotheses about the characteristics of these stars caused Hubble’s stress value to vary from 69 to 73.
By combining the aforementioned methods and uncertainties, the average Hubble stress value equal to 69.96 was obtained with an uncertainty of four percent. This margin of error overlaps with the theoretical prediction of the expansion rate of the universe, as well as the higher value of Tim Reiss.
Tensions and resolutions
The James Webb Space Telescope has provided methods for measuring the Hubble constant. The idea is simple: closer galaxies look more massive; Because you can make out some of their stars, while more distant galaxies have a more uniform appearance.
A method called gravitational convergence is more promising. A massive galaxy cluster acts like a magnifying glass, bending and magnifying the image of a background object, creating multiple images of the background object when its light takes different paths.
Brenda Fry, an astronomer at the University of Arizona, is leading a program to observe seven clusters with the James Webb Space Telescope. Looking at the first images they captured last year of the G165 cluster, Fry and his colleagues noticed three spots that were not previously seen in the images. These three points were actually separate images of a supernova that was located in the background of the aforementioned cluster.
After repeating the observation several times, the researchers calculated the difference between the arrival times of the three gravitational lensing images of the supernova. This time delay is proportional to Hubble’s constant and can be used to calculate this value. The group obtained an expansion velocity of 75.4 km/s/Mpa with a large uncertainty of 8.1%. Fry expects the error bars to correct after several years of similar measurements.
Both Friedman’s and Reiss’ teams predict that they will be able to get a better answer with James Webb’s observations in the coming years. “With improved data, the Hubble tension will eventually be resolved, and I think we’ll get to the bottom of it very quickly,” Friedman says.
James Webb vs. Hubble; Comparing the images of two space telescopes
The James Webb Space Telescope is now the flagship of the world of space telescopes. James Webb uses the largest mirror of any telescope launched into space and orbits the Sun at a distance from Earth (approximately 1.5 million kilometers). This telescope is supposed to make a big change in astronomy and astrophysics by looking at the farthest parts of the world and unveiling new secrets.
However, in the past three decades, the Hubble Space Telescope has been the main player in the field of space telescopes. Launched in 1990, this telescope has recorded many epic images of planets, stars, galaxies, nebulae and many other astronomical wonders.
Since Hubble was in near-Earth orbit, it could take accurate pictures of the universe without the Earth’s atmosphere interfering with its operation. The telescope captured amazing images during its prolific career and continues to serve its mission. According to NASA, over the past 32 years, Hubble has made 1.5 million observations and contributed to more than 19,000 scientific papers.
Now James Webb is going to take the flag from Hubble and further enhance our understanding of the universe. In a blog post comparing the two space telescopes, NASA called James Webb the “scientific successor” to Hubble. Without Hubble’s observations of the cosmos, researchers would not have prioritized building a telescope that could go beyond Hubble’s field of view. Continue with Zoomit to have a closer look at the images of celestial targets in both telescopes.
Deep field
The top right photo is the deep Hubble wallpaper taken in 1995 and released in 1996. At the time of recording, this photo was considered the deepest image taken of the universe. In order to make it, the researchers took 342 photos during 10 days with a total of 100 hours of exposure. The final result revealed more than three thousand scattered galaxies in a very small part of the sky. Over the next few decades, Hubble operators took better pictures of this type and looked much deeper into space.
The Hubble Ultra Deep Image or XDF was released in 2012.
The photo above is the Hubble Ultra Deep Wallpaper released in 2012. More than 5500 galaxies are visible in this photo. Over the course of a decade, the researchers collected 50 days of observations from a concentrated area, resulting in two million seconds of exposure (over 23 days).
Then along came James Webb. The first full-color scientific photo by James Webb was released on Tuesday morning Iran time by US President Joe Biden as a preview for the first set of telescope images. While capturing Hubble’s deep fields required days, if not weeks, of exposure, James Webb managed to capture this image after just 12.5 hours of exposure.
The recorded area of the sky in the image above is incredibly small; So small that it is about the size of a grain of sand on a person’s hand on the ground. In that part of the sky, a galaxy cluster called SMACS 0732 is located 4.6 billion light-years away. This cluster is so large that it bends space-time around it and, like a cosmic microscope, reveals faint galaxies far behind it. Some of these galaxies are considered to be the faintest infrared objects ever observed, and scientists are eagerly waiting to learn more about them.
Shahabhi Nebula (Karina)
The image above shows one of Hubble’s most popular targets, the Carina Nebula, at a distance of 7,200 light years from us. The image on the right, released by the Hubble Heritage Project in 2008, shows part of the star-forming region in the corner of the nebula.
The picture looks like an impressionist landscape with hills, valleys, and columns of gas and dust scattered around, with only a few bright stars behind the nebula. Now James Webb’s updated image shows the same stunning landscape in much greater detail and clarity. In the photo, there are stars that were previously hidden behind gas and dust.
Read more: Why is Jupiter one of the first targets of the James Webb Space Telescope?
Stephan’s quintuplets
This group of five galaxies is stunning in a Hubble image taken in 2009 after the telescope’s camera was upgraded earlier that year. That year, the space shuttle made its fifth and final visit to Hubble and applied a major upgrade. In addition to the new camera that took this photo, the telescope was also upgraded and repaired. The ability of astronauts to rendezvous with Hubble in near-Earth orbit kept the space telescope operational for a very long time.
However since James Webb is so far from Earth, he will not have the advantage of meeting astronauts. However, the spacecraft has enough fuel for at least 20 years; This means that in the future we will see many more images like the one above.
The photo above shows a group of galaxies that were first observed in 1877. The upper left galaxy is considered the alien mass of the group and is much closer to Earth than the other four members. However, the other four galaxies are so close that James Webb can see the shock waves from the interaction between them as they kill each other.
Stephen’s quintuplet is the largest image taken by the James Webb Telescope and is actually a mosaic made up of more than a thousand separate images captured by the telescope’s two instruments: the Near Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI). Both cameras collect infrared wavelengths of light and help James Webb see through gas and dust; But as their names suggest, both collect different wavelengths of infrared light.
Southern Ring Nebula
The last image is the Southern Ring Nebula, which was imaged by Hubble in 1998. The “ring” is the dying star particles (the faintest of the two bright spots in the center of the image). The little white dwarf causing all this chaos was a star the size of our Sun. At some point, the star ran out of fuel and ejected its outer layers, creating the ring seen in the image. The diameter of the ring is about half a light year and the gases are moving outward at a speed of nearly 14.5 km/s.
On the left, the Southern Ring Nebula is seen through the eyes of James Webb’s two instruments, Nirkem and Miri. The image we have chosen for comparison was captured by Nirkam’s near-infrared camera. Another version of the image is also recorded in mid-infrared.
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