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Our backyard black hole (Science Advent 9)

(Every day until December 25, I’m posting a science-related image and description.)

Day 9

The Milky Way's black hole, known as Sagittarius A*, in radio (blue) and X-ray (magenta) light. The radio data shows a strong hint of a jet emanating from the black hole. [Credit: X-ray: NASA/CXC/UCLA/Z.Li et al; Radio: NRAO/VLA]

The Milky Way’s black hole, known as Sagittarius A*, in radio (blue) and X-ray (magenta) light. The radio data shows a strong hint of a jet emanating from the black hole. [Credit: X-ray: NASA/CXC/UCLA/Z.Li et al; Radio: NRAO/VLA]

Nearly every large galaxy — a category including our Milky Way — harbors a black hole at its heart. These black holes are supermassive, weighing in at millions or billions of times the mass of the Sun. Their growth and evolution are intimately connected to that of their host galaxies, though we’re not completely sure how yet; similarly, their formation is still an intriguing mystery.

However, not every one of these monsters is “active”. The black holes gorging on matter are known as active galactic nuclei (AGN), and depending on the angle at which we view them are known as quasars, blazars, Seyfert galaxies, or other names. Our galaxy’s black hole, known as Sagittarius A* (pronounced “ay star”), is quiet. In that way, it’s like most galaxies in our cosmic neighborhood: the age of vigorous black hole activity corresponded to an earlier era, where there was more raw material to feed upon.

That’s not to say Sagittarius A* doesn’t have something going on. A recent set of observations shows that it might have a jet. Jets are tight streams of particles shaped by powerful magnetic fields, which are produced by swirling plasma around the black hole. In the case of active galaxies, jet activity can make black holes into some of the brightest objects in the Universe. In the case of the Milky Way, the possible existence of a gentler jet is a sign that even quiescent black holes can still have some life in them.

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