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The hunt for a new kind of black hole

Illustration: Eniola Odetunde/Axios

Astronomers have found indirect evidence of a new type of black hole, and they're now making advances toward seeing one for the first time.

Why it matters: Known as intermediate-mass black holes, these mysterious objects could be the key to unlocking how galaxies evolved, revealing more about why our universe looks the way it does.

The big picture: Black holes are an extreme laboratory by which sweeping theories can be put to the test.

  • They are where the laws of cosmology, general relativity and quantum physics that govern the largest and smallest processes in the universe combine.
  • If there is another type of black hole out there that astronomers have yet to discover, it will play a critical role in piecing together how our universe evolved, experts say.

Details: Scientists think intermediate-mass black holes may exist, but it's not clear how they form or where exactly they might be hiding today.

  • These types of black holes — which are thought to be about 100–100,000 times the mass of the Sun — are too large to have formed during the death of a star but too small to be considered supermassive black holes like the one found in the center of the Milky Way.
"If you have a small and a large, it's weird to just not have the medium."
— NASA astronomer Varoujan Gorjian told Axios

Where it stands: Astronomers have found dozens of possible intermediate-mass black holes, yet none have been confirmed.

  • The LIGO and Virgo detectors are sensitive enough to pick up on gravitational waves sent out during the collision of two intermediate-mass black holes.
  • Astronomers also hope that X-ray observatories could detect how these black holes might affect gas, dust and other objects around them, however, the light emitted during feeding frenzies may not be quite luminous enough to see from Earth with our current tools.
  • Gravitational waves "would give you the smoking gun, that direct measurement of the mass of these objects," LIGO's Salvatore Vitale told Axios.

Yes, but: If they do collide, intermediate-mass black holes likely produce strong gravitational waves at a frequency that competes with seismic activities on Earth — like cars driving by or waves crashing on the shore — making them harder for LIGO and Virgo to distinguish.

What's next: The European Space Agency's LISA mission — expected to launch in the mid-2030s — will be able to measure mergers between intermediate-mass black holes even in the distant universe, hopefully giving scientists an answer to the mystery once and for all.

Go deeper: Event Horizon Telescope hopes to produce first-ever moving image of a black hole