The universe is a damn big place. When we look at the night sky, almost everything that is visible to the naked eye is part of our galaxy: a star, a cluster of stars, a nebula. Behind the stars of the Milky Way, for example, the Triangulum galaxy peeps through. We find these "island worlds" everywhere in the universe, wherever we look, even in the darkest and most empty patches of space, if we can only gather enough light to look deep enough.
Most of these galaxies are so far away that even a photon traveling at the speed of light would take millions or billions of years to traverse intergalactic space. Once it was emitted from the surface of a distant star, and now it has finally reached us. And although the speed of 299,792,458 meters per second seems incredible, the fact that we have only traveled 13.8 billion years since the Big Bang means that the distance that light has traveled is still finite.
You probably think that the most distant galaxy from us should be no further than 13.8 billion light years from us, but that would be a mistake. You see, in addition to the fact that light moves at a finite speed through the universe, there is another, less obvious fact: the fabric of the universe itself expands over time.
Solutions general theory relativity, which ruled out such a possibility altogether, appeared in 1920, but the observations that came later - and showed that the distance between galaxies is increasing - allowed us not only to confirm the expansion of the Universe, but even to measure the rate of expansion and how it changed over time . The galaxies we see today were much farther away from us when they first emitted the light we receive today.
The EGS8p7 galaxy currently holds the record for remoteness. With a measured redshift of 8.63, our reconstruction of the universe tells us that the light from this galaxy took 13.24 billion years to reach us. A little more math and we'll find that we're seeing this object when the universe was only 573 million years old, just 4% of its current age.
But because the universe has been expanding all this time, this galaxy is not 13.24 billion light-years away; in fact, it is already 30.35 billion light years away. And do not forget: if we could instantly send a signal from this galaxy to us, it would cover a distance of 30.35 billion light years. But if you instead send a photon from this galaxy towards us, thanks to dark energy and the expansion of the fabric of space, it will never reach us. This galaxy is already gone. The only reason we can see it with the Keck and Hubble telescopes is that light-blocking neutral gas in the direction of this galaxy turned out to be quite rare.
Hubble mirror compared to James Webb mirror
But don't think that this galaxy is the most distant of the most distant galaxies we'll ever see. We see galaxies at such a distance as far as our equipment and the Universe allow us: the less neutral gas, the larger and brighter the galaxy, the more sensitive our instrument, the farther we see. In a few years, the James Webb Space Telescope will be able to see even further, because it will be able to capture light of a greater wavelength (and therefore with a large redshift), it will be able to see light that is not blocked by neutral gas, it will be able to see dimmer galaxies than our modern telescopes (Hubble, Spitzer, Keck).
In theory, the very first galaxies should appear with a redshift of 15-20.
Studying the most distant galaxies can show us objects billions of light-years away, but even with perfect technology, the spatial gap between the distant galaxy and the Big Bang will remain huge.
When we peer into the Universe, we see light everywhere, at all distances that our telescopes can only see. But at some point we will run into limitations. One of them is superimposed by the cosmic structure that is forming in the Universe: we can only see stars, galaxies, etc., only if they emit light. Without it, our telescopes can't see anything. Another limitation, when using forms of astronomy that are not limited to light, is the limitation of how much of the universe is available to us from the moment big bang. These two quantities may not be related to each other, and it is on this topic that our reader asks us a question:
Why is the CMB redshift in the range of 1000 when the largest redshift of any galaxy we've seen is 11?First, we must deal with what has been happening in our universe since the Big Bang.
The observable universe may stretch 46 billion light-years in all directions from our point of view, but there are certainly other parts of it that we cannot observe, and perhaps they are even infinite.
The whole set of what we know, see, observe and interact with is called the “observable Universe”. There are likely more regions of the universe beyond it, and over time we will be able to see more and more of these regions when light from distant objects finally reaches us after a cosmic journey of billions of years. We can see what we see (and more, not less) thanks to a combination of three factors:
- A finite amount of time has passed since the Big Bang, 13.8 billion years.
- The speed of light, the maximum speed for any signal or particle moving through the universe, is finite and constant.
- The very fabric of space has been stretching and expanding since the Big Bang.
Timeline of the history of the observable universe
What we see today is the result of these three factors, together with the original distribution of matter and energy, working according to the laws of physics throughout the history of the universe. If we want to know what the universe was like at any early point in time, all we have to do is observe what it is today, measure all the parameters involved, and calculate what it was like in the past. To do this, we will need a lot of observations and measurements, but Einstein's equations, while difficult, are at least unambiguous. The output results in two equations, known as the Friedmann equations, and the problem of solving them is one that every student of cosmology faces directly. But we, frankly, managed to make some amazing measurements of the parameters of the Universe.
Looking in the direction of the north pole of the Milky Way Galaxy, we can look into the depths of space. Hundreds of thousands of galaxies are labeled in this image, and each pixel is a separate galaxy.
We know how fast it is expanding today. We know how dense matter is in any direction we look. We know how many structures form at all scales, from globular clusters to dwarf galaxies, from large galaxies to their groups, clusters and large-scale filamentary structures. We know how much normal matter, dark matter, dark energy, as well as smaller components, such as neutrinos, radiation, and even black holes, are in the Universe. And only from this information, extrapolating back in time, can we calculate both the size of the universe and its rate of expansion at any point in its cosmic history.
Logarithmic plot of the size of the observable universe versus age
Today, our observable universe spans about 46.1 billion light-years in all directions from our point of view. At this distance is the starting point of an imaginary particle that set off at the moment of the Big Bang, and, traveling at the speed of light, would arrive at us today, 13.8 billion years later. In principle, at this distance all the gravitational waves left over from cosmic inflation were generated - the state that preceded the Big Bang, set up the Universe and provided all the initial conditions.
The gravitational waves created by cosmic inflation are the oldest signal of all that mankind could, in principle, detect. They were born at the end of cosmic inflation and at the very beginning of the hot Big Bang.
But there are other signals in the Universe. When it was 380,000 years old, the residual radiation from the Big Bang stopped scattering free charged particles as they formed neutral atoms. And these photons, after the formation of atoms, continue to experience redshift along with the expansion of the Universe, and they can be seen today with a microwave or radio antenna / telescope. But due to the rapid expansion of the Universe in its early stages, the "surface" that "glows" to us with this residual light - the cosmic microwave background - is only 45.2 billion light-years away. The distance from the beginning of the universe to where the universe was 380,000 years later is 900 million light years!
The cold fluctuations (blue) in the CMB are not colder per se, but simply represent areas of increased gravitational pull due to increased matter density. The hot (red) regions are hotter because the radiation in these regions lives in a shallower gravity well. Over time, denser regions are more likely to grow into stars, galaxies, and clusters, while less dense regions are less likely to do so.
It will be a long time before we find the most distant of all the galaxies in the universe we have discovered. Although simulations and calculations show that the very first stars could form in 50-100 million years from the beginning of the Universe, and the first galaxies - in 200 million years, we have not yet looked that far back (although, there is hope that after the launch in next year space telescope. James Webb, we can do it!). For today space record owns the galaxy shown below, which existed when the universe was 400 million years old - just 3% of its current age. However, this galaxy, GN-z11, is only 32 billion light-years away, about 14 billion light-years from the "edge" of the observable universe.
The most distant of all the discovered galaxies: GN-z11, photo from the GOODS-N observation made by the Hubble telescope.
The reason for this is that at the beginning, the rate of expansion dropped very rapidly over time. By the time the galaxy Gz-11 existed as we observed it, the universe was expanding 20 times faster than it is today. When the CMB was emitted, the universe was expanding 20,000 times faster than it is today. At the time of the Big Bang, as far as we know, the universe was expanding 1036 times faster, or 1,000,000,000,000,000,000,000,000,000,000,000,000 times faster than today. Over time, the rate of expansion of the universe has greatly decreased.
And for us it is very good! The balance between the primary rate of expansion and the total amount of energy in the universe in all its forms is perfectly maintained, up to the error of our observations. If the universe had had even a little more matter or radiation in its early stages, it would have collapsed back billions of years ago and we wouldn't be here. If there had been too little matter or radiation in the universe early on, it would have expanded so rapidly that particles would not be able to meet each other to even form atoms, let alone more complex structures such as galaxies, stars, planets, and humans. . The cosmic story that the Universe tells us is the story of the extraordinary balance by which we exist.
The intricate balance between the rate of expansion and the overall density of the universe is so delicate that even a 0.00000000001% deviation in either direction would make the universe completely uninhabitable for any life, stars or even planets at any given time.
If our best current theories are correct, then the first true galaxies should have formed between 120 and 210 million years old. This corresponds to a distance from us to them of 35-37 billion light years, and a distance from the farthest galaxy to the edge of the observable universe of 9-11 billion light years today. It's extremely far and says one thing amazing fact: The universe expanded extremely rapidly in the early stages, and today it is expanding much more slowly. 1% of the age of the Universe is responsible for 20% of its total expansion!
The history of the universe is full of fantastic events, but since inflation ended and the Big Bang happened, the rate of expansion has plummeted, and is slowing down as the density continues to decrease.
The expansion of the Universe stretches the wavelength of light (and is responsible for the redshift we see), and the large speed of this expansion is responsible for the large distance between the microwave background and the most distant galaxy. But the size of the universe today reveals something else astonishing: the incredible effects that have occurred over time. Over time, the universe will continue to expand more and more, and by the time it is ten times its current age, the distances will have increased so much that we will no longer be able to see any galaxies except for members of our local group, even with a telescope equivalent to Hubble. Enjoy all that is visible today, the great variety of what is present on all cosmic scales. It won't last forever!
At the edge of the galaxy
The most distant space objects are located so far from Earth that even light years is a ridiculously small measure of their remoteness. For example, the closest cosmic body to us - the Moon is located only 1.28 light seconds from us. How can one imagine the distances that a light pulse cannot overcome in hundreds of thousands of years? There is an opinion that it is incorrect to measure such a colossal space with classical quantities, on the other hand, we have no others.
The most distant star of our Galaxy is located in the direction of the constellation Libra and is removed from the Earth at a distance that light can overcome in 400 thousand years. It is clear that this star is located near the boundary line, in the so-called zone of the galactic halo. After all, the distance to this star is approximately 4 times the diameter of the imaginary expanses of our Galaxy. (The diameter of the Milky Way is estimated to be about 100,000 light-years.)
beyond the galaxy
It is surprising that the most distant, rather bright star was discovered only in our time, although it was observed earlier. For incomprehensible reasons, astronomers did not pay attention special attention on a faintly luminous spot in the starry sky and different on a photographic plate. What happens? People see a star for a quarter of a century and ... do not notice it. More recently, American astronomers from the Lowell Observatory discovered another of the most distant stars in the peripheral limits of our Galaxy.
This star, already dimmed from "old age", can be searched in the sky in the constellation of Virgo, at a distance of about 160 thousand light years. Such discoveries in the dark (in the literal and figurative sense of the word) parts of the Milky Way make it possible to make important adjustments in determining the true values of the mass and size of our star system in the direction of their significant increase.
However, even the most distant stars in our galaxy are relatively close. The most distant quasars known to science are more than 30 times further away.
A quasar (English quasar - short for QUASi stellAR radio source - “quasi-stellar radio source”) is a class of extragalactic objects characterized by very high luminosity and such a small angular size that for several years after discovery they could not be distinguished from “point sources” - stars.
Not so long ago, American astronomers discovered three quasars, which are among the "oldest" objects in the universe known to science. Their distance from our planet is more than 13 billion light years. Distances to distant space formations are determined using the so-called "red shift" - a shift in the emission spectrum of fast moving objects. The farther they are from the Earth, the faster, in accordance with modern cosmological theories, they move away from our planet. The previous distance record was set in 2001. The redshift of the then discovered quasar was estimated at 6.28. The current trinity has offsets of 6.4, 6.2 and 6.1.
dark past
Open quasars are only 5 percent "younger" than the Universe. What happened before them, immediately after the Big Bang, is difficult to fix: hydrogen, formed 300,000 years after the explosion, blocks the radiation of the earliest space objects. Only an increase in the number of stars and the subsequent ionization of hydrogen clouds allows us to break the veil over our "dark past".
To obtain and verify such information, it is required teamwork several powerful telescopes. The key role in this matter belongs to the Hubble Space Telescope and the Sloan Digital Telescope, located at the New Mexico Observatory.
On the boundless expanses of the Internet, I somehow stumbled upon the following picture.
Of course, this small circle in the middle of the Milky Way is breathtaking and makes you think about many things, from the frailty of being to the boundless size of the universe, but still the question arises: how much is all this true?
Unfortunately, the compilers of the image did not indicate the radius of the yellow circle, and estimating it by eye is a dubious exercise. However, the @FakeAstropix tweeters asked the same question as me and claim that this picture is correct for about 99% of the stars visible in the night sky.
Another question is, how many stars can be seen in the sky without using optics? It is believed that up to 6,000 stars can be observed from the surface of the Earth with the naked eye. But in reality, this number will be much less - firstly, in the northern hemisphere we will physically be able to see no more than half of this number (the same is true for residents southern hemisphere), and secondly, we are talking about ideal observation conditions, which in reality are almost impossible to achieve. That alone is worth one light pollution of the sky. And when it comes to the farthest visible stars, then in most cases, in order to notice them, we need exactly ideal conditions.
But still, which of the small twinkling points in the sky are the most distant from us? Here's the list I've managed to put together so far (although of course I wouldn't be surprised if I missed a lot, so don't judge too harshly).
Deneb- the most bright Star in the constellation of Cygnus and the twentieth brightest star in the night sky, with an apparent magnitude of +1.25 (it is believed that the limit of visibility for the human eye is +6, a maximum of +6.5 for people with really excellent eyesight). This blue-white supergiant, which lies between 1,500 (latest estimate) and 2,600 light-years away from us - thus the Deneb light we see was emitted somewhere between the birth of the Roman Republic and the fall of the Western Roman Empire.
The mass of Deneb is about 200 times the mass of our star than the Sun, and the luminosity exceeds the solar minimum by 50,000 times. If he were in the place of Sirius, he would sparkle in our sky brighter than the full moon.
P Cygnus dressed in red
Mu Cephei also known as Herschel's Garnet Star, is a red supergiant, perhaps the largest star visible to the naked eye. Its luminosity exceeds that of the sun by 60,000 to 100,000 times, and the radius, according to recent estimates, may be 1,500 times that of the sun. Mu Cephei is located at a distance of 5500-6000 light years from us. The star is at the end of its life path and soon (by astronomical standards) will turn into a supernova. Its apparent magnitude varies from +3.4 to +5. It is believed to be one of the reddest stars in the northern sky.
Plaskett's Star is located at a distance of 6600 light years from Earth in the constellation Monoceros and is one of the most massive systems double stars in milky way. Star A has a mass of 50 solar masses and a luminosity 220,000 times that of our star. Star B has about the same mass, but its luminosity is less - "only" 120,000 solar. The apparent magnitude of the star A is +6.05 - which means that theoretically it can be seen with the naked eye.
System This keel is located at a distance of 7500 - 8000 light years from us. It consists of two stars, the main of which is a bright blue variable, is one of the largest and most unstable stars in our galaxy with a mass of about 150 solar masses, 30 of which the star has already managed to drop. In the 17th century, Eta Carina had a fourth magnitude, by 1730 it became one of the brightest in the constellation Carina, but by 1782 it again became very faint. Then, in 1820, a sharp increase in the brightness of the star began and in April 1843 it reached an apparent magnitude of −0.8, becoming for a while the second brightest star in the sky after Sirius. After that, the brightness of Eta Carina plummeted, and by 1870 the star was invisible to the naked eye.
However, in 2007 the star's brightness increased again, reaching magnitude +5 and becoming visible again. The current luminosity of the star is estimated to be at least a million solar and it seems to be the main candidate for the title of the next supernova in the Milky Way. Some even believe that it has already exploded.
In conclusion, it is worth mentioning that there have been cases in history when people have been able to observe much more distant stars. For example, in 1987 in the Large Magellanic Cloud, located at a distance of 160,000 light years from us, a supernova broke out, which could be seen with the naked eye. Another thing is that, unlike all the supergiants listed above, it could be observed for a much shorter period of time.
Astronomers from Texas A&M University and the University of Texas at Austin have discovered the most distant galaxy known to us. According to spectrography, it is located at a distance of about 30 billion light years from solar system(or from our Galaxy, which in this case is not so significant, because the diameter of the Milky Way is only 100 thousand light years).
The most distant object in the Universe has received the romantic name z8_GND_5296.
"It's amazing to know that we are the first people in the world to see it," said Vithal Tilvi, PhD, co-author of the paper, which is now available online (for free viewing). scientific works use sci-hub.org).
The discovered galaxy z8_GND_5296 formed 700 million years after the Big Bang. Actually, in this state we see it now, because the light from the newborn galaxy has only now reached us, having traveled a distance of 13.1 billion light years. But since the Universe was expanding in the process, at the moment, as calculations show, the distance between our galaxies is 30 billion light years.
In newborn galaxies, it is interesting that there is an active process of formation of new stars. If in our Milky Way one new star appears per year, then in z8_GND_5296 - about 300 per year. What happened 13.1 billion years ago, we can now easily observe through telescopes.
The age of distant galaxies can be determined from the cosmological redshift caused, among other things, by the Doppler effect. The faster the object moves away from the observer, the stronger the Doppler effect becomes. The galaxy z8_GND_5296 showed a redshift of 7.51. About a hundred galaxies have a redshift greater than 7, meaning they formed before the universe was 770 million years old, and the previous record was 7.215. But only for a few galaxies, the distance is confirmed by spectrography data, that is, by the Lyman alpha spectral line (more on that below).
The radius of the universe is at least 39 billion light years. It would seem that this contradicts the age of the Universe at 13.8 billion years, but there is no contradiction, given the expansion of the very fabric of space-time: there is no speed limit for this physical process.
Scientists do not quite understand why other galaxies under 1 billion years old cannot be observed. Distant galaxies are observed by a clear manifestation of the spectral line L α (Lyman alpha), which corresponds to the transition of an electron from the second energy level to the first. For some reason, in galaxies younger than 1 billion years, the Lyman alpha line is becoming weaker. One theory is that just at that time the universe was transitioning from an opaque state with neutral hydrogen to a translucent state with ionized hydrogen. We simply cannot see the galaxies that are hidden in the "fog" of neutral hydrogen.
How did z8_GND_5296 manage to break through the neutral hydrogen fog? Scientists speculate that it ionized the immediate vicinity so that the protons could break through. Thus, z8_GND_5296 is the very first galaxy known to us that emerged from the opaque mess of neutral hydrogen that filled the Universe in the first hundreds of millions of years after the Big Bang.