Enlarge / No, that’s not an oddly shaped black hole. It’s a molecular cloud, which absorbs most wavelengths of light, making it hard to see what’s inside. (credit: FORS Team, 8.2-meter VLT Antu, ESO)
The biggest object in our galaxy is remarkably difficult to see. The core of our galaxy houses a supermassive black hole that weighs in at over a million times our Sun’s mass. And when it’s actively feeding on matter, it should be very bright. Yet for years, all we knew was that there was some sort of radio source there.
Evidence of a black hole at the center of our galaxy came indirectly by tracking the orbit of a nearby star. This demonstrated that there had to be something extraordinarily heavy in a very small region of space, strengthening the case that the object was an immense black hole.
Now, researchers are making a similar case for what may be the second-biggest black hole in the Milky Way. The object appears to be buried in a gas cloud that’s keeping it obscured. But the gas itself is moving fast enough that calculations suggest that a 100,000 solar-mass black hole is holding it together. That would make the object an intermediate-mass black hole. While intermediate-mass black holes play a key role in many cosmological models, we have yet to confirm any actually exist.
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