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After posts about giant hornets which can dissolve flesh with their stings, a huge asteroid passing by Earth, and a mass cemetery in New York City, it is hard to know what to write about next… Thankfully, astronomers are way ahead of me! This week featured the announcement that scientists have discovered a black hole “right in our backyard.”
Fortunately, what counts as our backyard to astronomers is not really our backyard by any quotidian definition. Located in the southern constellation Telescopium, the newfound black hole is 1,000 light-years away: although it is the closest black hole to Earth discovered thus far, it is still 9.5 quadrillion kilometers away (5.88 quadrillion miles). We probably won’t blunder into it by accident when we sneak downstairs for a midnight snack.
Black holes, as you know, are deformed patches of spacetime where gravity is so strong that all proximate matter and electronic radiation (like light) are pulled into the gravity well. Black holes form when exceedingly massive stars collapse at the end of their life cycle: they become more massive as additional matter accretes into them. For example the supermassive black hole at the center of the galaxy is believed to have the mass of 431 million suns!
The black hole’s orbit in the star system is marked in red
The newly discovered Telescopium black hole is nothing like that though. Scientists estimate its mass to be mere 4 to 5 times that of the sun. Astronomers were able to discover the object only because the other two stars in its solar system (which they were studying in order to better understand binary stars) were not orbiting each other in a comprehensible fashion. Some massive third party was implicated…yet nothing was visible. Ergo, a black hole. There are believed to be hundreds of millions or even billions of these invisible horrifying objects in our galaxy alone, but they are nearly impossible to find unless there are nearby objects for them to interact with (yet which have not been slurped down into the ravenous maw).
I wonder where the actual closest black hole to Earth is located? Maybe we don’t really want to find out…
Hey, did anybody notice there is a massive spooky ghost galaxy right next door to us? Well, actually the answer turns out to be “no: not really…not until November of last year.” It was only in November of 2018 that astronomers discovered Antlia 2, a galaxy which is a mere 130,000 light-years away from the Milky Way–which really is right next door in terms of cosmic distances (to contextualize this number, the diameter of the Milky Way itself is between 150,000 and 200,000 light years).
Ant2, as it is affectionately (?) called, is closer than the Large Magellanic Cloud, a dwarf galaxy with 30 billion stars which is 163,000 light years away and is generally regarded as our closest galactic neighbor. How did we miss this thing? And why are we calling it a ghost galaxy (aside from the fact that that sounds impossibly cool)?
Antlia 2 is a weird sort of celestial object. It has the lowest “surface brightness” of any known galaxy and is approximately 100 times more diffuse than any known ultra diffuse galaxy. Gee! that is really extremely diffuse. Antlia 2 is also a dark matter galaxy: the exiguous stars of which it consists are insufficient to hold it together without a great deal of unknown mystery mass. The ghost galaxy may be more than 99 percent dark matter. Additionally, Ant2 (insomuch as it exists) is hidden by the occlusion cloud above the spiral of the Milky Way. Only with the advanced astrometry readings of the European Space Agency’s satellite observatory Gaia were astronomers finally able to pinpoint this dark shadow in the sky above the southern constellation Antlia (which itself is named after an 18th century air pump).
What the jazz? This post is making less sense than usual, but I am not making any of it up…
I worry that this post is too abstruse for comfort. It concerns an all-but-invisible phantom galaxy made of unknown dark matter. The only reason we even found it to begin with is that astronomers were on the lookout for a hidden galaxy. Some unknown mass must have caused the stylish ruffles in the spiral arms of our own bright & lively Milky Way. Thus the fashion sensibility of space topologists helped us to find Antlia 2. Remind me about this thing in October. I want to draw some ghost galaxies to celebrate Halloween this year!
Previously discovered dwarf satellite galaxies (in blue) and the newly discovered candidates (in red) (Yao-Yuan Mao, Ralf Kaehler, Risa Wechsler (KIPAC/SLAC))
We have some new galactic neighbors! Well, actually maybe “new” is not the right term: they have been there for a long time but we only just now noticed. Astronomers are reporting the discovery of nine dwarf satellite galaxies orbiting the Milky Way like remoras stuck to a cosmic shark. These nine miniature galaxies are additional to the well-known Large and Small Magellanic Clouds—two dwarf galaxies which are located right next to the Milky Way (being respectively 160,000 and 200,000 light years away).
The new dwarf galaxies were discovered by a team of astronomers poring over data recovered from the Dark Energy Survey (a super-high resolution digital array which is part of the Victor M Blanco telescope in the Andes). The closest is a mere 97,000 light years from the Milky Way whereas the farthest lies 1.2 million light years away from us. The dwarf galaxies are a billion times fainter than the Milky Way. They are made up of millions (or hundreds of millions or even billions) of stars but are insignificant in size compared to the hundreds of billions of stars which constitute a true galaxy. Scientists believe that there are hundreds of similar miniature galaxies and pseudo-galaxies near the Milky Way, but they are dark and difficult to find (comparitively speaking).
The Large and Small Magellanic Clouds, near which the satellites were found. (image from European Southern Observatory)
I have been saying “dwarf galaxies” because I like the way it sounds (like the new galaxies live together in the woods in a little hut and work in the mines!), but actually only three of the new companions are definitely dwarf galaxies. The remaining six structures may be dwarf galaxies or they may merely be globular clusters—a far less euphonic phrase which indicates a group of stars which orbits a galactic core as a satellite. Unlike globular clusters, dwarf galaxies are held together by the gravitational mass of large quantities of dark matter (um, assuming it actually exists). Indeed dwarf galaxies seem to contain far greater quantities of dark matter than actual galaxies. This makes the newly discovered galactic neighbors a potentially useful focus for studying the properties of dark matter and refining our model of the universe.
A Composite Image of M104–The Sombrero Galaxy–taken from the Hubble Space Teelscope in Summer of 2003 (click on the image for a full-sized version)
Today I am posting some pictures of what I think is the most beautiful deep space object. The Sombrero Galaxy (M104) is a nearby galaxy which is visible edge-on in the constellation of Virgo. Actually, calling it an object might be a bit misleading since M104 consists of more than 400 billion stars–not to mention numerous associated globular clusters, innumerable planets, immense clouds of gas & gas, and a supermassive black hole which lies in the center. The black hole in the center of M104 isn’t a mild mannered & quiescent black hole like the one in the center of the Milky Way either. Based on the speed of revolution of the stars near the middle of M104, astronomers calculate that the central black hole has a billion times the mass of the sun.
An Infrared false-color image of the Sombrero Galaxy
In cosmic terms, the Sombrero galaxy is nearby—which is to say it is merely 28-odd million light years away. The galaxy was discovered in the late eighteenth century by Pierre Méchain . Other prominent 18th century astronomers subsequently observed and studied M104, including Charles Messier (which is the reason the galaxy is included in the “Messier” catalog and has a M-designation) and the redoubtable William Herschel who noted a “dark-stratum” bounding the luminous central bulge. We now know that this ring around M104 is a toroid dust lane of vast proportions which halos the galaxy. Astronomers initially thought that the Sombrero Galaxy was an unbarred spiral galaxy, but thanks to observations from NASA’s Spitzer space telescope (an infrared scope orbiting Earth), the scientific community has revised their estimation of its size upward. It lies somewhere between a spiral galaxy and an elliptical galaxy. In other words, when you look at the Sombrero Galaxy, you are looking at something vast beyond human comprehension—a galaxy bigger than our own filled with who knows what things we will never know. And yet if you expand the Hubble photo at the top of this post, you will see that all of the little stars shining around M104 are other galaxies farther away.
Olé!
ferrebeekeeper 