Massive Star’s Quiet Demise: Black Hole Formation Observed Without Supernova
- In a groundbreaking observation, astronomers have directly witnessed a massive star in the Andromeda Galaxy bypass the typical supernova explosion and collapse directly into a black hole.
- The star, located approximately 2.5 million light-years away, initially brightened in infrared light in 2014, as detected by NASA’s NEOWISE mission.
- “This star used to be one of the most luminous stars in the Andromeda Galaxy, and now it was nowhere to be seen,” explains Kishalay De, an associate...
Astronomers Witness Star’s Quiet Collapse into Black Hole, Challenging Supernova Paradigm
In a groundbreaking observation, astronomers have directly witnessed a massive star in the Andromeda Galaxy bypass the typical supernova explosion and collapse directly into a black hole. The event, designated M31-2014-DS1, provides an unprecedented opportunity to study the formation of stellar black holes and is reshaping our understanding of how massive stars end their lives. The findings, published , in the journal Science, detail a slow-motion cosmic fade-out rather than the dramatic, energetic outburst expected from such a stellar death.
The star, located approximately 2.5 million light-years away, initially brightened in infrared light in , as detected by NASA’s NEOWISE mission. However, by , its brightness plummeted, decreasing rapidly over less than a year. By and , the star had become nearly invisible in visible and near-infrared wavelengths, fading to one ten-thousandth of its original brightness. Currently, it’s only detectable in mid-infrared light, emitting roughly one-tenth of its initial intensity.
“This star used to be one of the most luminous stars in the Andromeda Galaxy, and now it was nowhere to be seen,” explains Kishalay De, an associate research scientist at the Simons Foundation’s Flatiron Institute and lead author of the study. “Imagine if the star Betelgeuse suddenly disappeared. Everybody would lose their minds! The same kind of thing [was] happening with this star in the Andromeda Galaxy.”
A Quiet Implosion, Not an Explosion
Traditionally, massive stars – those at least ten times the mass of our sun – are thought to end their lives in a spectacular supernova explosion. As the star exhausts its nuclear fuel, gravity overwhelms the outward pressure generated by fusion, causing the core to collapse. This collapse often triggers a shockwave that blasts the star’s outer layers into space, creating a supernova. However, M31-2014-DS1 defied this expectation.
Instead of exploding, the star’s core directly collapsed into a black hole, with its outer layers gradually pushed outward. This process, while theoretically predicted, has been rarely observed. The detailed observations of M31-2014-DS1, combining data from NEOWISE with observations from other ground and space telescopes spanning over a decade, provide the most comprehensive view yet of this type of stellar black hole formation.
The Role of Convection in a Failed Supernova
Researchers believe that convection – the circulation of gas driven by temperature differences within the star – played a crucial role in this quiet collapse. The core’s collapse initiates motion in the outer layers, preventing them from immediately falling into the newly formed black hole. Instead, these layers circulate around the black hole, with the outermost layers being pushed outward.
Andrea Antoni, a Flatiron Research Fellow and co-author of the study, explains that this convective motion slows down the rate at which material falls into the black hole. “The accretion rate — the rate of material falling in — is much slower than if the star imploded directly in. This convective material has angular momentum, so it circularizes around the black hole. Instead of taking months or a year to fall in, it’s taking decades.”
As this expelled material travels outward, it cools and forms dust, which absorbs energy and re-emits it in infrared wavelengths, creating a lingering reddish glow. This glow is expected to persist for decades, offering a prolonged opportunity for observation with telescopes like the James Webb Space Telescope.
Revisiting NGC 6946-BH1 and a Broader Picture
The analysis of M31-2014-DS1 prompted a re-examination of another previously identified object, NGC 6946-BH1. The team found that both stars followed a similar evolutionary path, suggesting that this quiet collapse mechanism may be more common than previously thought. What initially appeared as an unusual case now appears to be part of a broader category of “failed supernovae” that quietly produce black holes.
“We’ve known for almost 50 years now that black holes exist,” says De, “yet we are barely scratching the surface of understanding which stars turn into black holes and how they do it.”
The lingering infrared signal from the debris surrounding the newborn black hole in M31-2014-DS1 is expected to remain visible for years to come, providing a unique benchmark for understanding stellar black hole formation in the universe. De believes this is “just the beginning of the story,” and that continued observation will refine our understanding of these enigmatic cosmic events.