Webb Just Saw The Farthest Star Ever And It’s Mind Blowing

The James Webb Space Telescope has marked the  beginning of a new era in extragalactic astronomy. Within a few weeks of working, the infrared  observatory has already discovered several candidate galaxies that challenge the big bang  theory and our galactic evolution models. And now, Webb focused its instruments on the most distant  isolated star known in the universe, Earendel. The light-travel distance to Earendel is 12.9 billion  light years. This means that if the big bang is true, the star existed when the universe was just  900 million years old. Earendel might belong to a rare population of stars that astronomers  have been hunting for over half a century. But how did scientists discover a lone star  so far away in the universe? How is Earendel different from the stars we see around?  Finally, and most importantly, how do the recent James Webb observations of Earendel  challenge our theories of stellar evolution? The light travel distance to  Earendel is 12.9 billion light years, but the present proper distance, which considers  the universe’s expansion, is 28 billion light years. So we are actually looking at the star  as how it appeared 12.9 billion years ago. This means that Earendel is about 8.2 billion  years older than the Sun and the Earth. So far, the smallest objects observed at  these distances were star clusters embedded in distant galaxies. But Earendel is the first  isolated star found at such a large distance. This star was discovered by chance  using the Hubble Space Telescope. Hubble first observed the star’s parent galaxy  that was gravitationally lensed by a cluster in the foreground. Massive astronomical objects such  as galaxy clusters distort the spacetime fabric around them. As a result of this distortion,  the light from the foreground celestial bodies bends when it passes close to these massive  objects. In certain cases of precise alignment, the foreground clusters can magnify the light  from individual stars by factors of thousands. Because of this gravitational lensing, the  background galaxy containing Earendel appeared like an arc that the astronomers named the Sunrise  arc. But the team saw a bright object sitting on the edge of the distorted galaxy. Luminous sources  in distant galaxies tend to be highly energetic events such as novas, supernovas, or tidal  disruptions caused by black holes. These are transients that happen to change their brightness  with time. However, Hubble’s observations showed that the brightness of this object remained  constant for over three and a half years. Hence, astronomers concluded it’s a gravitationally  lensed bright star in Sunrise Arc. Because of its wavelength limitations, Hubble  could provide only limited information about this distant star. So astronomers used the  James Webb Space Telescope to study Earendel’s properties further. This study was led by Dr.  Brian Welsh from Johns Hopkins University. He discovered the star with his team in March  2022 using the Hubble Space Telescope data. In their paper, the researchers analyzed new  images of Earendel obtained by Webb’s NIRCam instrument. These images span a wavelength range  of 0.8 to 5 microns. Earendel was studied in eight different Webb filters, with each filter  having an exposure time of over half an hour. There are three significant points  to note in the new observations by the James Webb Space Telescope.  The first is the star’s redshift. The redshift of deep space objects  gives a measure of their distance. Redshift is denoted by a dimensionless  quantity z. Z = 0 marks present time, and as its value increases, so does the  lookback time and the distance to that object. New Webb observations confirm that  Earendel lies at a redshift of 6.2. This number is consistent with  the Hubble Space Telescope data released in early 2022, making Earendel  the highest-redshift star ever. The next important thing to note about  Earendel is its bolometric luminosity, or the energy emitted by the star over  the entire electromagnetic spectrum. The Webb data rules out the possibility of  Earendel being a low-mass star, a brown dwarf star, or a free-floating exoplanet that got  gravitationally lensed. Instead, the data show that it’s a B-type star with an effective surface  temperature of 13,000-16,000 kelvin. Stars in the universe are chiefly divided into seven categories  based on their surface temperatures: O, B, A, F, G, K, and M. One can remember the sequence with  a classic mnemonic: Oh, be a fine girl, kiss me. The problem lies when we calculate  the total luminosity of Earendel, which is between 600,000 to one million times  the luminosity of the Sun. This means that if Earendel is a single evolved star, its mass must  be about 40 times that of the Sun. Alternatively, this light could be produced by two stars of 30  solar masses or five stars of 20 solar masses if one assumes a surface temperature of about 15000  kelvins. Researchers note in their paper that a single-star solution is not the only one that can  explain the Spectral Energy Distribution plots. And that’s why the possibility that Earendel  is a multiple-star system cannot be ignored. Massive stars that we see around in the local  universe often have companions and frequently have more than one companion. While the primary  companions lie within two astronomical units of the star, the tertiary companions can  be as far as 20 astronomical units. This means that even if  Earendel has companion stars, they cannot be seen by the James Webb  telescope because of the resolution power. Another problem is that if the star is one  million times more luminous than the Sun, it will exceed the Humphreys-Davidson limit  or the HD limit. The HD limit is the empirical luminosity limit above which no stars have  been observed, at least in the local universe. So if Earendel is confirmed to be a single  star a million times the luminosity of the Sun, we might have to reconsider the HD  limit and place new constraints on it. Earendel’s discovery is important because this  might be the first observation of a Population III star that astronomers have been hunting for  decades. Primordial nucleosynthesis produced two major chemical elements: hydrogen and  helium. The first generation of stars, known as population III stars, had trace amounts  of metals and hence, a low metallicity. In astronomy, any element other than hydrogen  and helium is referred to as a metal. Astronomers believe that most of the population  III stars have died by now, and the remaining ones are pretty dim and difficult to observe.  They are almost impossible to be seen naturally, and most candidates have been found  in gravitationally lensed galaxies. Astronomers expect that Earendel will remain  highly magnified for years to come. The following observation of Earendel using the James Webb  Space Telescope is scheduled for December 2022. Accurate measurement of Earendel’s  brightness and surface temperature would narrow down its type and stage in the  stellar lifecycle. Astronomers also expect to find that the Sunrise Arc galaxy lacks heavy elements  that form in subsequent generations of stars. It would strongly suggest Earendel  is a rare, massive metal-poor star. Looking for the first stars and galaxies has been  a holy grail in astronomy. The discovery of the first generation of stars would help us understand  star formation and verify the predictions made by the big bang model. Also, searching for  them is like searching for our own origins; as Richard Feynman once said, “The most  remarkable discovery in all of astronomy is that the stars are made of atoms  of the same kind as those on Earth.” This concludes the 23rd episode  of the Sunday Discovery Series. If you enjoyed this video, make sure  to like it, subscribe to our channel, and press the bell icon so that you don’t  miss any future episodes of this series.

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