A massive star’s core will collapse when it runs out of energy. The collapse of the core releases neutrinos that cause a shockwave to travel through all layers. The outer layers can be blasted into space if the shock wave is powerful enough. The outer layers will fall onto the core if the shock is weak. It continues to fall until it becomes a blackhole, at which point the star vanishes.
Astronomers have reported observations in a recent study of M31 2014-DS1, a supergiant with a depleted hydrogen content, located within the Andromeda Galaxy. Recently, astronomers witnessed the death quietly of a massive star. The star did not explode in glory like a supernova.
Instead, it faded and collapsed into a dark hole. Scientists were able to watch the last chapter in a cosmic story unfold live, and it is the most clear record of how stars transform into the darkest mysteries of the universe.
The story was pieced together by using new observations as well as data that goes back more than 10 years. The observations confirmed theories that have been around for a long time: the core of the star gave way and sank into a dark hole while its outer layers unraveled slowly, drifting out into space.
Scientists published the findings in Science on 12 February. They are exciting. Astronomers have been able to trace the steps of how stars disappear into black holes and others explode as brilliant supernovae for the first time. This is a rare look at the endings and beginnings of stars.
Kishalay de, associate researcher at Simons Foundation Flatiron Institute, and the lead author of the new study said. This is only the beginning.
The light from the dusty debris that surrounds the black hole will be visible at telescopes with a high sensitivity, like the James Webb Space Telescope for many decades. It’s because the light is going to fade slowly. This could be a milestone in understanding the formation of stellar black holes throughout the universe.
Astronomers have been studying the M31-2014 star, located in Andromeda galaxy, some 2.5 million light years from Earth. They watched the star through NASA’s NEOWISE Project and other telescopes for years.
The star started to shine brighter, in infrared, in 2014 as though it was gaining strength. In 2016, the star’s brightness dimmed drastically, just two years after it first appeared.
In 2022 or 2023 the star was all but gone.
It was nothing more than a shadow in visible or near-infrared, and only one-tenth of its former brightness. It is now a ghostly, tenth of the power that it once was, visible only under mid-infrared.
De says, This star was once one of the brightest stars in the Andromeda Galaxy. Now it’s gone. Imagine the sudden disappearance of Betelgeuse. Everyone would go crazy! It’s the same thing!
[was] “What’s happening to this star in Andromeda Galaxy?”
Astronomers have compared observations to long-standing theories, and they found that there is strong evidence the star has collapsed into black holes.
The stars glow because hydrogen is fusing into helium at their cores. This fusion generates an outward force that counteracts gravity.
This equilibrium can be upset if a star that is ten to one times as heavy as our Sun runs out of energy.
Gravity crushes a star when it takes control. The star is crushed by gravity when the core collapses.
This release of neutrinos can cause a shockwave that can rip the star in half. Sometimes the shock wave is weak. The outer layers of the star fall inward instead, piling up onto the neutron stars until they become a blackhole.
The fading star appears to have taken the quieter route, sliding into darkness and leaving only the telltale sign of a new black hole.
Black holes have been known to exist for over 50 years. Says De We are only scratching the surface in terms of what stars become black holes, and how.
M31-2014 DS1 allowed astronomers to rethink the fate of another fading stellar, NGC 6946 BH1. Convection was the missing puzzle piece. It is the constant movement of warm and cold gases within a star.
The star’s core is hot, but its outermost layers are cool. The gases are set in motion by this difference, and they rise and fall like water boiling.
The outer layers of the black hole were still moving with convective motion when the core collapsed.
The innermost layers spun around the blackhole instead of falling into it. The swirling was able to push away the outermost layer, which ejected them into space. The material that was expelled cooled as it drifted away and became dust.
This dust covered the gas that surrounded the black hole. It also radiated faintly with infrared. The lingering glow of red can last for many decades.
It is a silent afterimage left by a vanished star.
Andrea Antoni was a Flatiron Research fellow who had predicted that convection could change how stars collide. Her ideas became a reality with the help of new data from M31 2014-DS1. She said that material entering the black hole is moving much slower than anticipated. The swirling gas, instead of pushing straight into the black hole, is circling it like water around a drain.
The collapse is spread over years rather than months.
It doesn’t happen immediately. It shines brighter and slowly dims for a short time. Moving gases inside the star (known as convection), prevent the collapse to happen all at once.
This material falls bit by bit backwards as it keeps on circling the black hole.
Only about 1 percent of outer star gas is actually fed to the black hole. This tiny amount of gas is sufficient to make the black hole glow faintly.
Astronomers revisited NGC 6946 – BH1, a fading star that was first observed ten years earlier, by reexamining the M31-2014 – DS1. It’s now clear that what was once an unusual case is part of a family of dying stars, which collapse into black holes and leave behind long glowing afterimages.
Reference to Journal:
- Kishalay De, Morgan Macleod, Jacob Jencson et al. The formation of a Black Hole is responsible for the disappearance of an enormous star from Andromeda Galaxy. Science. DOI: 10.1126/science.adt4853
