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Ep. 28, Page 34
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Comic 2084 - Ep. 28, Page 34

18th Feb 2016, 11:57 PM in Episode 28 :: Save My Place | Load My Place
Average Rating: 5 (2 votes)

Author Notes:

smbhax 18th Feb 2016, 11:57 PM edit delete
Thanks to a couple readers for sending me links to various articles (this story really got around!) on a new mass estimate for the supermassive black hole at the center of galaxy NGC 4889, 308 million light years from Earth. Most of the articles suggested or even said that this black hole was the biggest one ever found, but it isn't; according to Wikipedia's list of most massive black holes, NGC 4889's 21 billion solar mass black hole ranks in at number 5.

The ESA's original news release on the weighing of NGC 4889's black hole is here; it mentions that its mass was estimated by measuring the velocity of stars moving around it—this is the same way that the supermassive black hole at the center of our own galaxy, the black hole known as Sagittarius A*, was discovered and weighed (at a comparatively minuscule 4 million solar masses): in 2002, star S2 ("Source 2") was observed moving as close as 17 light-hours to the central mass, and by the end of 2008, a total of 16 years of observing it and other stars moving around the center revealed S2's orbit, mass, and velocity, and from that, scientists were able to calculate that the gravity necessary to whip the star around in an elliptical orbit at speeds exceeding 5000 kilometers per second (11 million miles per hour, 1.67% the speed of light—"the fastest known ballistic orbit") could only be generated by an extremely compact mass of about 4 million Suns—and that could only be a supermassive black hole.

S2 takes 15.5 years to complete its orbit around A*. In 2012, a much fainter star was noticed in an even tighter orbit around the black hole: S102 completes its orbit in just 11.5 years. And I found something else I hadn't known in S2's Wikipedia article: "it is believed that there are thousands of stars, as well as dark stellar remnants (stellar black holes, neutron stars, white dwarfs) distributed in the volume through which S2 moves." So even though science had only charted the orbits of 28 or so stars around A* as of 2008, the very center of the galactic core is thought to be a much busier place than we can currently see; a close study of the motions of the stars there that we can see can potentially start picking out some of these other objects, as they should cause slight perturbations in their orbits.

Oh, and I do recommend looking through that list of the most massive black holes, it's pretty interesting. More and more will be found all the time, of course, but the current chart-topper is the cryptically named S5 0014+81, the estimated 40 billion solar mass black hole at the center of a blazar—a very compact quasar, the huge radio-wave-emitting storm at the center of a galaxy whose central black hole is actively sucking down vast quantities of material: S5 0014+81 is thought to be swallowing 4000 Suns worth of material each year! The energy radiating out of the storm of hypervelocity material swirling around it renders it "25 thousand times as luminous as all the 100 to 400 billion stars of the Milky Way Galaxy combined, making it one of the most powerful objects in the universe"—but it can only be seen through telescopes because it is 12.1 billion light years away from us—and this means that it is also very old (the universe as a whole being only about 14 billion years old), which "suggests that supermassive black holes grow up very quickly." (It should be noted, mind you, that estimating the hole's mass from the light emitting from its accretion disc is less reliable than estimating the mass by the orbital velocity of objects around it, so its 40 billion solar mass weight is a less reliable figure than the ones for many of the black holes on the chart below it.)

But there's lots of other cool stuff in that list, for instance the estimated 10 billion solar mass black hole at the center of galaxy MS 0735.6+7421 has been causing an eruption of huge wings of hot gas for the last 100 million years; the clouds of gas and the detected gamma ray bursts from this storm are so large that if the eruption has been caused by material accreting into the black hole, the amount of material needed would be equivalent to 600 million Suns! However, the eruption could possibly have been caused by the rotation of the black hole.

And there's the 4 billion solar mass black hole at the center of the Hercules A galaxy, shooting out plasma jets over 1 million light years in length! (Cool composite visible light / radio wave photo picture there.) (The mere 55 million mass hole in Galaxy Centaurus A powers jets that long as well; material shoots along them at 50% light speed!)

And while the big blazar mentioned above is pretty far away, the 2 billion solar mass black hole at the center of quasar ULAS J1120+0641 has a comoving distance of 28.85 billion light years! That's possible, even though the galaxy is under 14 billion years old and nothing can travel faster than the speed of light, because the universe is also expanding at all points in all directions: so, while the light has really only traveled 12.9 billion light years as we measure light years today, since it was emitted from the quasar, "less than 770 million years after the Big Bang, about 13 billion years ago," that 12.9 billion light year distance has expanded along with the rest of the universe, so the quasar today is actually 28.85 billion light years away, making it the most distant and earliest quasar known, and quite an item of interest for theories about the Big Bang, because it is so old that it would have been around before the universe became ionized, and light could move around freely—indeed, this and other quasars could have been prime movers in that theorized "reionization" of the universe, the end of the "Cosmic Dark Ages." It also may help explain its unusual composition: while other quasars (even the next oldest, just 100 million years younger) have less than 1% of their hydrogen in a neutral, non-ionized state, ULAS J1120+0641 contains 10 to 50% neutral hydrogen, and no noticeable quantity of metals that would have formed after the initial Big Bang nucleosynthesis, which suggests that it was "embedded in a protogalaxy in the midst of forming, [...] or a pre-protogalaxy core still embedded in the primordial hydrogen fog," maybe just in the process of generating what would be the universe's first stars.

(Incidentally, if you want to see an even older galaxy (but not a quasar), here's one that's 30 billion light years away. The light from this one is so old—13.1 billion years—that it would have been generated at the tail end of those "Cosmic Dark Ages," and thus would normally have been absorbed in the primordial plasma, not surviving to reach our eyes; one theory is that the light had some help, and a nearby "population of smaller, undetected galaxies, contributed to the reionization."

Using the gravitational lensing effect of intervening galaxy clusters, the Hubble Space Telescope has also spotted what may be an even more distance galaxy, MACS0647-JD, but could only estimate its distance by the rather crude technique of photometric redshift, which judges the expansion of its light by a broad range of colors, as opposed to more refined spectrographic analysis, which could break the light down into unique elemental signatures, whose shift could be much more precisely measured; confirmation of that galaxy's distance, and further detection of "galaxies more than 13.4 billion light years away, less than 300 million years after the Big Bang," cannot be accomplished by Hubble, and requires the improved low-wavelength detection that will provided by Hubble's successor, the infrared-specializing James Webb Telescope, due in 2018—only two years away, now!)


cattservant 19th Feb 2016, 1:57 AM edit delete reply
Hope she's narrowed the search already.
smbhax 19th Feb 2016, 10:29 PM edit delete reply
Well if not we'll just skip ahead a little ^_^
moizmad 19th Feb 2016, 12:04 PM edit delete reply
There's a room with a view!
smbhax 19th Feb 2016, 10:29 PM edit delete reply
Now that she installed one!