Shulou(Shulou.com)11/24 Report--

Thanks CTOnews.com netizen Hua Ke high achiever's clue delivery! In 2009, astronomers found that the brightness of a star 2000 million light-years away began to plummet. Later, no matter through the ground telescope or Hubble, Spitzer and other space telescopes, people never saw it again. Yes, this star just disappeared from our eyes!

Various speculations have been made about what happened to the star. Astronomers then pinned their hopes on the Weber (Webb) telescope (JWST), hoping it would help us solve the mystery. But when they saw the image data brought by JWST, the scientists made an unexpected discovery this time.

NGC 6946 is a spiral galaxy at the edge of the constellation Cygnus. The rate of star formation here is very high. Although the number of stars is less than half that of the Milky way, supernovae explode ten times as frequently as the Milky way, so it is also known as the "fireworks galaxy".

One day in 2009, astronomers discovered that the brightness of a star in the galaxy suddenly began to increase. Just two months later, the star's luminosity reached 1 million times that of the sun.

Judging from past experience, this should be a massive star at a late stage of evolution, and the sudden increase in brightness means that it may be about to usher in the highest luminous moment of its life-a supernova explosion. Given that it is likely to be close to 25 times the mass of the sun, this final explosion may be a rare extreme supernova explosion. If so, its luminosity could soar by several orders of magnitude, reaching a staggering tens of billions of times the luminosity of the sun.

However, while people were waiting to witness the splendor of the universe, its brightness began to decline, and then returned to its previous brightness. It seems to be a false alarm, maybe it's just a temporary brightness change caused by other reasons.

But soon it was discovered that something was wrong. The brightness of the star seemed to be declining all the time, and there was no sign of stopping. At this time, it is like a tungsten light bulb without power, and it soon loses its former brilliance.

By the next year, the star had completely disappeared from our view. Even through the Hubble Space Telescope, astronomers were not able to see it again. Only a little light in the infrared band seems to prove that it once existed.

How can such a huge star just disappear? In this regard, many scientists think that we may have encountered the legendary "failed supernova", a special way for stars to turn into black holes-direct collapse.

We know that in theory, when the mass of star debris exceeds the Oppenheimer limit (about 2.5 times the mass of the sun), star debris will collapse into a black hole. But this collapse is only the core of the star, and its outer material explodes directly into a supernova.

This is for stars with a mass of 8 to 25 times the mass of the sun before the explosion. If the metal content is not taken into account, if the star is more massive, then the theoretical explosion of the supernova may not be more violent, but calmer, or even no obvious explosion. This is because it has become the core of a black hole, which can directly pull back the material to explode and swallow it by virtue of its strong gravity. It shows that the star is about to explode, and the whole "whoosh" becomes a black hole, so it is also called a "failure supernova".

Is the star we are talking about today very similar to this failed supernova?

Previously, this phenomenon is only theoretical speculation, there has been a lack of actual observation evidence, so this time many astronomers believe that this star may be a legendary failed supernova. If that were the case, the star would not have disappeared, but would have quietly become a black hole. Because it is located in the galaxy NGC 6946, it has been named "N6946-BH1".

However, some scientists do not think so: although it is not visible in the visible band, it can still be seen in the infrared band. If it really becomes a black hole, where does all this infrared light come from? So the star may not have become a black hole at all, maybe it is just blocked by its own ejection of matter, like Betelgeuse darkened.

Well, if the light is so tightly blocked, how much material do you have to spray? I guess you'll have to take a break, don't you? And who says that if you turn into a black hole, you can't emit infrared? other people's eating plates (accretion plates) can also produce infrared.

Both sides have their own reasons, and it is impossible to determine who is right and who is wrong based on visible and near-infrared data for the time being. Maybe the mid-infrared can provide some clues. So in 2023, scientists pointed JWST at the location of the star.

Through JWST's mid-infrared imager (MIRI), it is clear that there is a bright signal source here. It is obvious that it is the star that has disappeared. But this still does not prove that the star is still alive, and we still need to look at the characteristics of the radiation lines.

Through the analysis of the energy distribution of the spectrum, the mid-infrared radiation spectrum emitted by the star seems to be consistent with the characteristic that the dust is irradiated by the star's ultraviolet rays. This suggests that the star may indeed be alive, just because of some unknown "small explosion" in which the ejected material obscures the short waves below the visible light in the stellar light, and only part of the infrared long wave radiates out.

But what kind of outbreak is it that can cover itself so tightly without blowing itself up? At this point, the researchers seem to have found the answer in the near-infrared image of JWST.

Thanks to the super resolution of JWST, the researchers found that the so-called massive star may not be a star, but a triad, a star system of three stars. Due to the limited ability of the previous equipment, people have always regarded them as a star.

So combined with this finding, the researchers made a more reasonable guess: this "star disappearance" event may be a more common phenomenon-the merger of stars. When two stars are about to merge, their respective outer envelopes are the first to merge, leading to an increase in luminosity in 2009. After that, a large amount of material from the two stars was ejected to form large tracts of dust, which obscured the visible light of these stars, and we found that they disappeared. If this guess is true, then when the dust dissipates in the future, we will see these stars again. It's just this time. It could be decades, hundreds of years, thousands of years, or more.

Although the explanation for this stellar merger seems more plausible, the evidence is still not straightforward enough, so the real reason behind the phenomenon is still inconclusive.

Since star collisions can lead to the temporary disappearance of stars, is the sudden disappearance of celestial bodies not the only one?

A few years ago, scientists launched a project called "sources that disappear and appear in a century of observation" (VASCO). As the name suggests, the purpose of the project is to look for celestial bodies that have suddenly disappeared or suddenly appeared over the past century, and then explore the reasons behind them. By comparing the data, the project identified 150000 candidates from data containing 600 million celestial bodies over the past 70 years. They then conducted the first manual screening of one of the 10 celestial bodies, and then identified 798 stars that suddenly disappeared.

Although there are certain possibilities for "failed supernovae" and "stellar jet occlusion", these speculations are far from explaining the disappearance of all celestial bodies. This shows that there are still many unknowns in the universe waiting for us to explore, among which we do not rule out the most attractive possibility-a more advanced alien civilization.

Reference:

[1] https://en.wikipedia.org/wiki/N6946-BH1

[2] https://en.wikipedia.org/wiki/NGC_6946

[3] https://en.wikipedia.org/wiki/Failed_supernova

[4] https://academic.oup.com/mnras/article/508/1/1156/6372931

[5] https://arxiv.org/abs/2309.16121

[6] https://iopscience.iop.org/article/10.3847/1538-3881/ab570f

[7] https://ui.adsabs.harvard.edu/abs/2022Univ....8..561V/abstract

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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