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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…
Sometimes if you aren’t watching the heavens (or the news) closely enough, you miss a major astronomical discovery. For example last summer, astronomers discovered a galaxy which formed only one or two billion years after the Big Bang (so I guess it is unclear whethter I missed this story by one year or by 12 billion). At any rate, the galaxy hunters used the Hubble space telescope to peer through a powerful gravitational lense far away in space. Gravitational lenses are areas where timespace is warped like a huge lense by high-gravity phenomena, and a viewer can use them like a huge lense to see far-away objects. By using the Hubble telescope together with the gravitational lense they were able to see back a dozen billion years in time to the edge of the universe…as it once was not long after creation. What they saw perplexed them.
There is a fundamental difference between galaxies. Galaxies where stars are being formed tend to be blue and spiral shaped (like our own beloved Milky Way!). Galaxies where stars have largely stopped forming are “red and dead” since the remaining stars tend to be long lived red dwarf stars and the bright young (short-lived) blue stars are mostly gone. These red galaxies are not shaped like spirals, but tend to be elliptical shaped (like an egg or a football, not like one of those evil gym machines).
The ancient galaxy at the edge of the universe was neither of those colors or shapes. It was a dense yellow disk. Stars formed in an (enormous) accretion disk but then, for some reason, new star formation stopped. The blue stars burned out (“the light that shines twice as bright etc, etc..”), but the yellow middle aged stars were still burning. The galaxy had three times the mass of the Milky Way but scrunched into a pancake of much smaller area.
So do galaxies always form as disks and then either become self-renewing blue spirals (maybe by colliding with other galaxies or clouds of dust)or dead red footballs? Or was this early yellow disk galaxy an abberation? Or is our own galaxy truly new (well…newish…being only a few billion years old)? I do not understand astrophysics well enough to answer these questions or even formulate them properly (although I get the sense some of these questions may not yet be answered by anyone in any comprehensive way), but I would love to hear what people can add to this rudimentary yet compelling story of shapes and colors.
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.
News of the cosmos frequently involves inconceivably large numbers or gigantic objects beyond human imagination. This is particularly true of galaxies–gigantic systems of stars, gas clouds, black holes, and exotic unknown dark matter. Even the tiniest dwarf galaxies have tens of millions of stars and our lovely home galaxy, the Milky Way, has approximately 300 billion star systems! However the universe is a mysterious place and it frequently refutes conventional wisdom and prior expectations. This week astronomers from Hawaii’s Keck Observatory announced that they had discovered a ridiculously little galaxy with only a thousand stars. The adorable miniature galaxy, which has been dubbed Segue 2 is not a star cluster because it is surrounded by its own halo of dark matter, but it is many orders of magnitude smaller than any known galaxy. Astronomers are trying to determine whether it is a scrap of a larger galaxy which was ripped apart (!) or whether it is a baby galaxy which never fully coalesced. Astronomers hope that by learning more about Segue 2 and other hypothesized tiny galaxies they can find out more about the creation of the universe and the formation of elements.
“NO!” –image editors
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