Star caught red-handed disappearing and turning into a black hole

The discovery will help explain why some massive stars turn into black holes when they die, while others do not.

A team of astronomers observed a dying star which did not explode as a supernova, but which turned into a black hole.

This remarkable observation is the most complete observational record ever made of the transformation of a star into a black hole, allowing astronomers to build a comprehensive physical picture of the process.

Combining recent observations of the star with more than a decade of archival data, astronomers have confirmed and refined theoretical models of how stars so massive turn into black holes.

The team discovered that the star didn’t explode like a supernova at the end of your life; Instead, the star’s core collapsed into a black hole, slowly expelling its turbulent outer layers in the process.

The results of the , published on February 12 in the journal Scienceare already generating enthusiasm as they constitute a rare glimpse of the mysterious origins of black holes. The discovery will help explain why some massive stars turn into black holes when they die, while others do not.

“This is just the beginning of the story“, it says Kishalay Deresearch associate at the Simons Foundation’s Flatiron Institute and lead author of the new study.

Light from the dusty debris surrounding the newborn black hole, says De, “will be visible for decades to the level of sensitivity of telescopes like the James Webb Space Telescope, because it will continue to disappear very slowly. And this could end up being a reference point to understand how stellar black holes form in the Universe.”

The now extinct star, called M31-2014-DS1is located about 2.5 million light years away from Earth, in neighboring Andromeda galaxy.

De and his collaborators analyzed measurements of the star taken by NASA’s NEOWISE project and other ground- and space-based telescopes over a period from 2005 to 2023.

They found that the infrared light from M31-2014-DS1 began to brighten in 2014. Then, in 2016, the star quickly fell far below of its original luminosity in just one year.

Observations in 2022 and 2023 showed that the star disappeared essentially in the visible and near infraredbecoming 10,000 times less bright at these wavelengths. Its remnant is now only detectable in the mid-infrared, where it shines with just one-tenth of its previous brightness.

“This star used to be one of the brightest of the Andromeda Galaxy and Now you can’t see it anywhere. Imagine if the famous star suddenly disappeared. Everyone would lose their minds! The same kind of thing was happening with this star in the Andromeda Galaxy,” says De.

Comparing these observations with theoretical predictions, the researchers concluded that the dramatic fading of the star to such a small fraction of its original total brightness constitutes strong evidence that its core collapsed and became a black hole.

The stars fuse hydrogen into helium in their coresand this process generates external pressure to balance the incessant internal pull of gravity.

When a massive star, about 10 or more times more massive than our Sun, it begins to run out of fuel, the balance between internal and external forces is disturbed. Gravity begins to collapse the star, and its core collapses first to form a dense neutron star at the center.

Often, the emission of neutrinos in this process generates a powerful shock wave that is sexplosive enough to tear through most of the core and the outer layers in a supernova.

However, if the neutrino shock wave fails to push the stellar material out, theory has long suggested that most of the stellar material would fall back into the neutron star, forming a black hole.

“We’ve known that black holes exist for almost 50 years“, says De, “but we have barely begun to understand which stars turn into black holes and how they do it.”

The observations and analysis of M31-2014-DS1 allowed the team to reinterpret observations of a similar star, . This led to an important breakthrough in understanding what happened to the outer layers surrounding the star after it failed to go supernova and collapsed into a black hole. The forgotten element? The convection.

Convection is a byproduct of large temperature differences inside the star. The material near the center of the star is extremely hot, while the outer regions are much cooler. This difference causes gases inside the star to move from hotter to cooler regions.

When the star’s core collapses, the gas in its outer layers continues to move quickly due to this convection.

Theoretical models developed by Flatiron Institute astronomers have shown that this fact prevents most of the outer layers from falling directly into the black hole; instead, the innermost layers orbit outside the black hole and drive the ejection of the outermost layers of the convection zone.

The ejected material cools as it moves away from hot material that surrounds the black hole. This cold material quickly forms dust as atoms and molecules combine.

Dust obscures hot gas that orbits the black hole, heating the dust and producing a glow observable at infrared wavelengths. This persistent red glow is visible for decades after the star itself disappears.

Andrea Antonico-author and Flatiron Institute Research Fellow, previously developed the theoretical predictions for these convection models.

With the impressive observational evidence from M31-2014-DS1, says Antoni, “the rate of accretion – the rate of material falling in – is much slower than if the star imploded directly inward. This convective material has angular momentum, so it circulates around the black hole.”

“Instead of taking months or a year to fallit’s taking decades. And because of all this, it becomes a brighter source than it would otherwise be, and we observe a long delay in the dimming of the original star,” he adds.

Just like water swirls around the drain of a bathtub instead of flowing straight down, the gas moving around this newly formed black hole continues in its chaotic orbiteven when it is slowly pulled in.

Thus, the slow fall generated by convection prevents the entire star from collapsing directly into the newborn black hole. Instead, the researchers propose that even after the core implodes, some of the material slowly falls away over many decades.

Only about 1% of the gas of the original stellar envelope falls into the black hole, feeding the light currently emanating from it, researchers estimate.

While analyzing observations of M31-2014-DS1, De and his team also reevaluated a similar star, , classified 10 years ago.

In the new scientific article, they present impressive evidence that explains why this star followed a similar pattern. M31-2014-DS1 initially stood out as a “bizarre object,” says De, but now it appears to be just member of an object class – including NGC 6946-BH1.

“Only with these individual jewelry of discovery That’s when we started to compose a picture like this”, says De.