Black holes, the colloquial name for massive gravitational singularities that exist in the universe, have been in the news a lot this past year. Scientists were able to use a massive planet-spanning network of radio telescopes to capture history’s first picture of a black hole. Now, astronomers are excited about another singularity-related discovery — a so-called ‘impossible’ black hole. What makes this singularity impossible, and what does it mean for our understanding of these celestial nightmares?
Stellar black holes like the impossible one that astronomers recently discovered are formed when a dying star explodes, a process called a supernova, before collapsing back in on itself. It becomes a gravitational singularity, pulling in everything around it, including light. These singularities come in two varieties — stellar and supermassive — though there is a third theoretical variety that falls between the two ends of the spectrum.
Supermassive black holes are the ones that sit at the center of spiral galaxies like our own and can be millions or billions of solar masses, meaning they essentially weigh billions of times what our home star does. These singularities are so large that we’re not quite sure how they formed.
Stellar black holes, on the other hand, have a limit. They are usually anywhere between 10 and 100 solar masses, though the ones in our Milky Way galaxy are usually smaller, measuring in at five to 20 solar masses.
Our sun is actually too small to become a black hole. When it reaches the end of its life cycle, it will expand into a red giant — wiping out the majority of the inner planets in the process — before collapsing back into a white dwarf. Luckily, that won’t happen for another five billion years or so.
That limitation on black hole size in the Milky Way galaxy is why scientists are so excited about the discovery of this impossible singularity.
LB-1 is a stellar black hole that resides roughly 15,000 light-years from Earth. While that wouldn’t normally be cause for celebration — scientists estimate there are anywhere between 10 million and a billion black holes in the Milky Way galaxy alone — there’s something that sets LB-1 apart.
It’s roughly 70 solar masses in size.
That’s nearly three and half times the size of every other black hole that we’ve discovered in the Milky Way, if you don’t count the supermassive one that rests at the heart of the galaxy. According to everything we’ve found so far, it shouldn’t exist here.
It’s impossible, and for astronomy, impossible means exciting.
What does the discovery of this massive black hole mean for astronomy?
For one thing, it means we have to re-examine the way we look at black hole formation. While it’s unfair to say that everything we know is wrong, it’s clear that we’re missing a few vital pieces of the puzzle that would facilitate our understanding of how these interstellar monstrosities are formed.
It’s possible that LB-1 is the result of the collision of more than one singularity, something that astrophysicists have theorized but as of yet have not witnessed. It’s also possible that because the star that birthed this singularity is part of a binary system, having the nearby fuel source allowed it to grow much larger than it would have otherwise managed.
The team that found LB-1 thought the large stars that are likely to become black holes at the end of their life shed much of their mass as they start to collapse and shouldn’t be able to create a singularity this large.
It’s an interesting puzzle and one that astronomers are eager to solve to advance our understanding of black holes, and of the universe around us.
There is so much about these massive singularities we don’t understand, from how the supermassive black hole at the heart of our galaxy formed, to how we’ll be able to spot them if we’re traveling through space and they’re not actively consuming a star. The discovery of LB-1 gives us another piece of the puzzle. We might not have found the edge pieces that will help us assemble it, but we’ve found enough to start seeing how the picture comes together.