When the largest stars die, it’s usually pretty obvious.
Supernovae are visible from billions of light-years away.
But recently astronomers watched a massive star just disappear.
No explosion, nothing, it just… vanished?
Of course, it could have been dust.
It’s always dust.
But one intriguing possibility is that the star just imploded directly into a black hole,
without the supernova detonation.
And if that’s the case, is this happening more often, we just didn’t notice it?
Stars, of course, are gigantic balls of hot plasma held in perfect balance.
Gravity compresses the star together heating it up to the point that fusion can happen
in the dense core.
Atoms of hydrogen are fused together in a variety of ways, eventually forming helium,
and this process is exothermic, which means that it releases energy in the form of gamma
radiation.
These photons push outward, bouncing around from atom to atom, holding back the gravitational
pull of all the stellar material.
As long as there’s fusion in the core, the star will remain a star.
Once a less massive star like our Sun runs out of hydrogen fuel in its core, it still
has enough heat and pressure to fuse heavier elements, but it eventually runs out of fuel,
blows off its outer layers, and becomes a white dwarf, eventually fading away to the
background temperature of the Universe.
Much more massive stars than the Sun have more fusion options available to them, creating
heavier and heavier elements in their core.
These continue to be exothermic reactions until the star starts to get iron in its core.
The fusion of iron isn’t exothermic, it’s the stellar equivalent of trying to burn ash
in your fireplace.
No additional energy is released, so the light pressure pushing outward suddenly shuts off.
Without that pressure, the star implodes in on itself, with the layers falling inward
at relativistic speeds.
As this infalling material reaches the core it instantly crashes together and creates
a neutron star or even a black hole.
The protons and neutrons collide together with enormous energy, releasing an enormous
amount of material and radiation into space.
This, of course, is a supernova.
Astronomers are still working out all the peculiarities of how supernovae work.
What kinds of stars explode in which ways and leave behind what kinds of remnants.
But they all go with a bang.
So they were surprised to find a star that would have been big enough to generate a powerful
supernova, and yet, it just disappeared.
The star was located in the Kinman Dwarf Galaxy, located about 75 million light-years away
in the constellation of Aquarius.
Astronomers have been actively studying this galaxy because it’s one of the most metal-poor
galaxies we know of, very low in the kinds of heavier elements that make up stars like
our Sun.
They were studying the galaxy intensively, between 2001 and 2011.
Although it’s too far away to study the individual stars in the galaxy, there were
able to detect the signatures of a few extreme objects.
They had noticed the signal of a massive star that was in the end stages of its life.
Classified as a “luminous blue variable” star, it’s about 2.5 million times brighter
than the Sun, and was broadcasting a specific kind of light that’s detectable.
This star was definitely going to explode as a supernova any day now, astronomically
speaking, tomorrow, or in tens of thousands of years (well, after the light takes 75 million
light-years to get here, of course).
In 2019, astronomers came back to study the galaxy again, this time with the world’s
most powerful telescope; the European Southern Observatory’s Very Large Telescope.
And much to their surprise, the star was nowhere to be found.
Even though it’s 75 million light-years away, astronomers see supernovae at that kind
of distance several times a year.
You can even see them in a backyard telescope.
No supernova was been reported in the Kinman Dwarf Galaxy.
The astronomers brought even more of the Very Large Telescope’s instruments to bear on
the galaxy, including the ESPRESSO instrument, and the X-shooter instrument.
Even using all 4 telescopes that make up the Very Large Telescope, they weren’t able
to detect anything.
In the 2011 data, there was an indication that the star was going through a period of
strong outbursts.
This could have released dust that obscures our view or transformed it into a less luminous
star.
Or maybe the star did something that’s not supposed to happen.
It turned directly into a black hole without exploding as a supernova first.
We’ll talk about that in a second, but first I’d like to thank:
Brenda Kalt E. Michael Kaiser
Marshall Mabry Tilleen
Shaun
And the rest of our 853 patrons for their generous support.
Want our videos early, with no ads?
Join our community at patreon.com/universetoday.
The current theories say that massive stars should all end in supernovae, but it’s actually
possible that 30% just collapse directly, without the explosion.
In fact, astronomers think they’ve seen something like this happen before.
Back in 2017, astronomers announced that a star with 25 times the mass of the Sun had
also disappeared.
It was located in the spiral galaxy NGC 6946, located about 22 million light-years from
Earth.
In 2009, it started to brighten significantly, but by 2015, it was just gone.
It had winked out of existence.
Astronomers turned the Hubble and Spitzer Space Telescopes on the galaxy, searching
for the star to see if it had just dimmed down.
Spitzer would have been able to see if it was being obscured by dust.
But nothing, no sign of it.
At the same time, astronomers saw six other nearby stars explode as a regular supernova,
leading to the estimate that 10-30% of massive stars fail to generate supernovae.
If stars are indeed avoiding the whole supernova process, it’s extremely exciting scientifically,
of course, but it might also help illuminate an even deeper mystery.
The most massive black holes in the Universe are the ones contained at the heart of most
galaxies.
Our own Milky Way has a supermassive black hole with 4.1 million times the mass of the
Sun.
Astronomers are constantly surprised at how supermassive black holes are being discovered
farther and farther out into the cosmos when the Universe was just a fraction of its current
age.
One of these supermassive black holes is a quasar with 800 million times the mass of
the Sun, which it had acquired just 690 million years after the Big Bang.
It’s hard to explain if you go the traditional path, with massive stars forming, exploding
as supernovae, and leaving behind black hole remnants that go on to merge together.
These stars generate powerful solar winds which can prevent nearby material from continuing
to fall in.
But if the material can collapse directly into black holes, without the pesky supernova
radiation, you could see more and more material come together directly.
Hundreds of thousands, maybe millions of times the mass of the Sun, turning directly into
a black hole.
So, if astronomers can find more of these objects, it’ll help explain one of the biggest
mysteries in astronomy.
So what happened to this blue luminous star?
Was it obscured due to dust, or did it collapse into a black hole?
It’s going to take a more powerful telescope, like the European Southern Observatory’s
Extremely Large Telescope, due for completion in a couple of years to actually resolve the
individual stars in the galaxy and see if there’s any sign of it.
Or maybe the Vera Rubin Observatory will see more stars just disappearing, providing more
evidence that the Universe really does strange things when we’re not looking.
What do you think?
Let me know your thoughts in the comments.
Here are the names of the Patrons who support us at the $10 level and more.
Want to see your name here and support the work we do?
Go to patreon.com/universetoday Newsletter:
Once a week I gather up all my space news into a single email newsletter and send it
out.
It’s got pictures, brief highlights about the story, and links so you can find out more.
Go to universetoday.com/newsletter to sign up.
Did you know that all of my videos are also available in a handy audio podcast format,
so you can have the latest episodes, as well as special bonus material like interviews
with me, show up on your audio device?
Go to universetoday.com/audio, or search for Universe Today on iTunes, Spotify, or wherever
you get your podcasts.
I’ll put a link in the show notes.
We got an answer to another mystery supernova earlier this year, where a star exploded inside
another star, producing one of the most luminous supernovae ever detected.
You can watch a video all about that now.