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Artist's Concept of WISE J224607.57-052635.0

Artist’s Concept of WISE J224607.57-052635.0

Ferrebeekeeper has featured some mind-bogglingly strange astronomic entities before—black holes, ultra-dense stellar remnants, hyper-giant stars with a million times the mass of the sun, colliding neutron stars—but today we move up to a vastly greater order of magnitude!  Astronomers have just discovered a new class of galaxy which emits energy at unimaginable levels.  Using NASA’s Wide-field Infrared Survey Explorer (WISE), scientists have discovered what are being tentatively called “extremely luminous infrared galaxies” (ELIRGs).

One of these galaxies (with the not-very-snappy designation “WISE J224607.57-052635.0”) is producing 10,000 times more energy than the Milky Way, despite being much smaller than our familiar home.  The newly discovered galaxy is putting out more energy than 10 trillion suns (or, more correctly, I should say it was putting out the energy of ten trillion main-sequence yellow stars). Scientists consider it the brightest known galaxy in the universe.

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WISE J224607.57-052635.0 is 12.5 billion light-years away.  Since the universe is 13.8 billion years old, what we are now seeing dates to a whole different era of galactic dynamics.  Today maybe WISE J224607.57-052635.0 is a burned-out remnant…or a perfectly respectable middle-aged galaxy like the Milky Way.  Who knows?  But twelve-and-a-half billion years ago it was releasing an inconceivable amount of energy—so much so that astronomers are having trouble adjusting their theories to it.  Perhaps some embryonic galaxies have black holes which gobble up stars at a much greater rate than initially thought or, alternately, some unknown set of circumstances has allowed the black hole (or holes?) at the center of WISE J224607.57-052635.0 to somehow surpass the theoretical threshold of black hole feeding.

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Clearly astronomers are going to be sorting out what exactly happened out there for quite a while, but in the meantime, when you look up at the night sky remember you are looking at an invisible fountain of energy ten trillion times brighter than the sun. [Ooh, I made myself dizzy]

Sirius, located in the constellation Canis Majoris

The brightest star in the night sky is Sirius.  Only 8.6 million light years from Earth, Sirius A is 25 times more luminous than the sun.  Because of its brightness, the star was well known in ancient times—it was named Sopdet in Ancient Egypt and it was the basis of the Egyptian calendar.  After a 70-day absence from the skies Sirius (or Sopdet) first became visible just before sunrise near the Summer solstice—just prior to the annual Nile floods.   Greek and Roman astronomers philosophized and speculated about Sirius, (which they called “the dog star” because of its closeness to the constellation Canis Majoris).  Arabs knew the star as Aschere “the leader”.  Polynesians used it as a principle focus of their astonishing oceanic navigation.  Over countless millennia, Sirius has worked its way deep into human consciousness as one of the immutable landmarks of the night sky.

Hieroglyph of Sirius/Sopdet

So imagine the shock when it was discovered that Sirius is not alone.  The bright star we know is actually Sirius A, a star with twice the mass of the sun. In 1844 the German astronomer Friedrich Bessel hypothesized a tiny companion for Sirius based on the irregular proper motion of Sirius.  Then, in 1862, as the American Civil war was being fought an American astronomer in Chicago first observed the tiny companion, Sirius B (thereafter affectionately known as “the Pup”). Sirius B has nearly the same mass as the sun (.98 solar mass) but it is only 12,000 kilometers (7,500 mi) in diameter—nearly the same distance around as Earth.

An Artist's Conception of Sirius A and Sirius B

Today Sirius B is the closest white dwarf star to planet Earth.  However it has not always been so, Sirius B began its life as a luminous blue B-type main sequence star with a mass five times that of the sun. About 124 million years ago—as the dinosaurs grazed on the first magnolias—Sirius B fused its way through the hydrogen and helium in its mass.  As Sirius B began to fuse together larger elements like oxygen and carbon it expanded into a red giant star with a diameter 10 to 100 times that of the sun. Then Sirius B ran out of nuclear fuel.  Without the heat generated by nuclear fusion to support it, the star underwent gravitational collapse and shrank into a hyper dense white dwarf star.  These tiny stars are extremely dense and hot when they are formed, but since they generate no new energy their heat and radiance gradually radiate away over billions of years until the stars are completely black and dead.

Not this sort of "White Dwarf"--Curse you Google Image Search!

Although Sirius B is largely composed of a carbon-oxygen mixture, its core is overlaid by an envelope of lighter elements. Hydrogen, being lightest, forms the outermost layer (which is why the little star currently appears uniformly white).

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October 2020