“Spots” orbiting Milky Ways central black hole


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Using the ALMA ground-based telescope array in Chile, astronomers have detected two energetic “spots” that appear to be orbiting Sagittarius A* (pronounced A-star), the super-massive black hole at the center of the Milky Way.

The spots appear to be regions in the accretion disk surrounding the black hole that are emitting energy.

Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein’s special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.

The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. “In general, the faster the movement is, the more difficult it is to take a photo of the object,” says Oka. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.” The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole.

Everyone please repeat after me: Though this scenario makes sense, based on the facts and our knowledge, there is a lot of uncertainty about these conclusions.

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