NGC 1277: Hubble Space Telescope image of galaxy that may have commandeered another galaxy’s supermassive black hole.Image: NASA/ESA/Andrew C. Fabian

Do black holes jump ship and wander off to other galaxies? If so, a galaxy called NGC 1277 may harbor a fugitive in its core. In 2012 astronomers discovered a supermassive black hole at its center with the mass of 17 billion suns—the most massive known. Normally, a black hole this enormous would be found in a much larger galaxy, which points to something unusual in NGC 1277’s past. Two astronomers have one idea: What if the black hole was captured after being spit out of a galactic collision billions of years ago?

In fact, the black hole may be a reject from an even larger nearby galaxy. Billions of years ago two galaxies—each carrying a black hole in its core—slammed together to form a massive galaxy called NGC 1275. During the collision, the central black holes spiraled together, merged and recoiled into intergalactic space. The newly coalesced homeless black hole wandered the Perseus galaxy cluster until NGC 1277 passed close enough to gravitationally ensnare it. “It is speculative, but it’s a fun story,” says Gregory Shields, an astronomer at The University of Texas at Austin and lead author on a paper in The Astrophysical Journal Letters proposing this scenario. “You don’t need to invent any new physics. You just need to have the luck to run into the smaller galaxy.”

via Are Galaxies Playing Catch with Black Holes?: Scientific American.

Eight of our nine dwarf planets and candidates, to scale, with their moons and our best guess of their colors. The top four are the acknowledged dwarves, the bottom four Brown’s proposed four. Ceres, not shown, is grayish and about the size of Sedna. Image credit: Wikimedia creative commons

One of my favorite shirts honors the brave souls of the former planet Pluto, those billion voices which shouted out in agony and were suddenly silent as the International Astronomical Union’s space station destroyed– wait, no. That’s not what happened to Pluto. Pluto got demoted from the ranks of “planet” to “dwarf planet” a few years ago, much to the dismay of students around the country. But what does that mean, why did it happen, and what are these dwarf planets, anyway? Today I’d like to take you on a tour of some of our Solar System’s smaller inhabitants, and walk you through the strange lands of extreme cold, dark, and quiet on its farthest shores.

What dwarf planets are

Let’s start with the reason Pluto got demoted in the first place. The problem was simple: we kept finding other things in the Solar System which were officially “asteroids,” but which were all about the size of Pluto, or even a bit bigger. It was starting to seem silly to call some of them planets (and give them lots of extra attention) and others not when it was becoming clear that they were all kind of alike. So instead, we defined a new category for them, the “dwarf planets.” By the current census, our Solar System therefore contains four gas giants: Jupiter, Saturn, Uranus, and Neptune; four terrestrial (“rockball”) planets: Earth, Venus, Mars, and Mercury; and five dwarf planets: Eris, Pluto, Makemake, Haumea, and Ceres. And there are actually many more; the census of dwarf planets is only beginning. Astronomers estimate that there are between one and two hundred dwarf planets orbiting our sun. Mike Brown of Caltech, one of the foremost experts in this field, lists four more that are likely to be added to the list soon: 2007 OR-10, Quaoar, Sedna, and Orcus. (Yes, one of these still needs a name.)

via You Haven’t So Much Lost a Planet, as Gained 5 Dwarves… | Guest Blog, Scientific American Blog Network.

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