After the existence and death of trillions of stars, the concept map of the early universe environment was formed. The existence and life cycle of stars are the main processes that make the universe not only rich in hydrogen and helium, but also the radiation emitted by the first star makes it transparent to visible light. Copyright: NASA/ESA/European Southern Observatory /Wolfram Freudling et al. (STECF)
Observing our universe today, it is estimated that there are two trillion galaxies in it, and each galaxy contains hundreds of billions of stars on average. This means that we can see about 10 24 stars in the visible universe, just like the greatest observatory of mankind, it can even "take us back" in theory. When we see farther and farther away, we are also looking back at time, because the Big Bang happened before a limited time (138 billion years), and the distance between seeing and seeing stars is limited. There must have been no stars for some time, so for some time, the first star appeared in the universe. When was that? Now I want to know the answer more than ever.
Because this distant galaxy, GN-z 1 1, is located in the region where most of intergalactic medium has been re-ionized, Hubble can now reveal it for us. James webb will be more detailed and see further in the future. Image copyright: NASA, ESA and A. Field (STScI).
Thanks to the greatest observatories of mankind, such as Hubble Space Telescope, behemoths on the ground 10 meters, and infrared space telescopes such as Herschel and Spitzer, mankind has seen more cosmic things than ever. We have discovered a series of galaxies and quasars from 65.438+0.2 billion years ago to 65.438+0.3 billion years ago, some of which are even earlier. The current record holder is GN-z 1 1. This galaxy only has the light of the universe 400 million years ago, and this galaxy is 3% of its present age. We can see this galaxy completely, and our current telescope is unlikely to find stars or galaxies farther than this. In the future, we need more powerful and sensitive telescopes!
Logarithmic scaling concept of Hubble volume. Please note that our time is limited to the visible time range, that is, the time since BIGBANG-65.438+038 billion years, or (including the expansion of the universe) 46 billion light years. There are no stars and galaxies here; For us, even in theory, there are limits. Copyright: Wikipedia user Pablo Carlos Buddas.
This is not because there are no stars or galaxies outside this range, but the nature of the universe at that time meant that we could not see those stars or galaxies that existed. Once the first 380,000 years have passed, the universe has cooled stably enough to form neutral atoms without being directly ionized by the residual radiation in the Big Bang. There are no stars at this time; ; It takes tens of millions of years (even more than 1 100 million years) of gravity to make these insignificant areas attract enough substances to ignite the first nuclear fusion, namely:
1. The universe is expanding, which means that even the hottest stars will produce ultraviolet rays with red shift: from ultraviolet rays to visible light to infrared rays, far exceeding what Hubble can see.
2. Now the universe full of neutral atoms blocks the light emitted by these stars, just as the neutral matter in our galaxy blocks the center of the Milky Way in our eyes.
The star density map of the Milky Way and the surrounding sky clearly shows the Milky Way and Magellanic Cloud. If we look closely, NGC 104 and NGC 6205 on the left side of SMC are slightly higher than and close to the left galaxy core, and NGC 7078 is slightly lower. However, in the case of visible light, the center of the Milky Way becomes blurred because of the absorption of light by neutral matter in the plane of the Milky Way. Image copyright: ESA/Gaia
And those first-generation stars and galaxies are different from ours. At present, the stars in the universe are composed of about 70% hydrogen, 28% helium and 1-2% "other substances", which astronomers call "metals". "If you look at the stars that once existed, condense hydrogen into helium and then convert helium into heavier elements, this is the sum of their functions: enriching the post-Big Bang universe, that is, 75% hydrogen, 25% helium and 0% metal, which is what we see today. This means that the first star formed should be primitive, or composed of hydrogen and helium, without other elements pollution. The best candidate we have now is a group of stars in the CR7 galaxy, whose light took 654.38+0.3 billion years to reach our eyes.
The illustration of the first discovered galaxy CR7 is considered to be the third generation star: the earliest star in the universe. JWST will show real images of this galaxy and other similar galaxies. Photo version: ESO/M. Kornmesser
We can simulate when the earliest conditions for nuclear fusion existed in the universe, so the first star.
Theoretically, we can use the known structure formation to simulate the formation time of the first stars, because modern science already knows the following points:
1. When the universe is 380 thousand years old, what is the density of some areas of the universe?
2. Both matter and radiation should obey the laws of physics (such as gravity and electromagnetism).
3. How many universes are made up of matter, radiation, dark matter and neutrinos?
4. And how to cool, shrink and collapse in the expanding universe.
Scientists can simulate the initial conditions in the universe, thus producing the ignition of nuclear fusion to produce the first/batch of stars.
These stars are invisible in the current observatory, because the neutral matter around them blocks too much emitted light. Before the universe is re-ionized, this means that there are enough hot ultraviolet-emitting stars to turn these neutral atoms into ionized plasma, which ultraviolet and visible light cannot penetrate. On average, the universe will not be re-ionized 50-55 billion years ago. The ancient galaxy gnz 1 1 is located in the space where re-ionization occurred in the early stage of our sight.
Generally speaking, what needs to be done is to observe the infrared part of the rest light, because neutral atoms are inefficient in shielding this point.
These four photos show four different wavelengths of light in the center of the Milky Way. The top wavelength is longer (sub-millimeter), and the Milky Way is terminated in the form of visible light through far infrared and near infrared (second and third). Note that dust bands and foreground stars blur the center of visible light. Image copyright: ESO/ATLASGAL Alliance/ NASA /GLIMPSE Alliance/VVV Sky Survey/ESA/Planck/D.Minniti/S. Thanks: ignacio Toledo, Martin Cohen Messer.
We can see this by observing our own galaxy. It may be opaque to visible light and ultraviolet light, but it is transparent at longer and longer wavelengths. This is why the James Webb Space Telescope has made such great progress. Yes, it's bigger than Hubble. Yes, it will have more advanced instruments. But the biggest leap will be that it is designed to see longer wavelengths, all the way to the middle infrared, about 20 times the longest wavelength that Hubble can see. Theoretically, it should be able to see the light of distant galaxies and clusters-as early as the age of the universe1.500 million to 250 million.
James webb will have seven times the concentrating power of the Hubble telescope, but he will be able to see farther in the infrared spectrum of the spectrum, revealing earlier galaxies than Hubble can see. Copyright: NASA /JWST Science Team
But there is more science to be done. Even in james webb, we can't go all the way to everyone's first star, but we may better handle where and when they are. As for the original primitive stars? The first star proved that there was nothing but hydrogen and helium. If nature is kind to us, james webb will not only bring us the first one, but also bring us many examples.
The universe is there waiting for us to discover it. If we want to know the answer, we just need to look. When we build better observatories and get better data, our understanding of all these data will only improve.