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Between giant planets and small stars exists a bizarre class of heavenly objects known as brown dwarfs. Brown dwarfs are not massive enough to fuse hydrogen elements together as do main sequence stars like the sun, however brown dwarfs larger than 13 Jovian masses are believed to fuse deuterium atoms and large brown dwarfs (65 Jovian masses and up) are believed to fuse lithium.  Since brown dwarfs can be very much like planets or like stars, there is a specific definition to describe the objects: a brown dwarf must have experienced some sort of nuclear fusion as a result of mass and temperature, however it cannot have fused all of its lithium (or it is considered a star or stellar fragment).  A stellar physicist reading this blog might object that medium and large stars have some lithium present in their outer atmosphere, or that a very young white dwarf could still have some unused lithium present, or even that an old heavy brown dwarf could have fused all of its lithium.  That physicist would be correct: she deserves some cookies and a pat on the head for poking holes in unnecessarily simple definitions.

Various Classifications of Brown Dwarfs

Various Classifications of Brown Dwarfs

Brown dwarfs were theorized to exist in the 1960s, but no astronomer managed to discover one until 1988 when a team of University of California astronomers who were studying white dwarfs found a bizarrely cool red spectral signature for a faint companion to the star GD 165.  Since then many brown dwarfs have been discovered and sorted into the major types M, L, T, and Y.  They occupy a strange ambiguous area at the bottom of the Hertzsprung-Russell diagram—objects which are luminous and massive in comparison to everything else but tiny and dim compared to real stars.

450px-Relative_star_sizes.svg

There are some planets which are known to orbit brown dwarfs and there also brown dwarfs known to orbit true stars.  It is beginning to seem that there a great many brown dwarfs out there: perhaps they are as numerous as true stars (or maybe they are even more common than that).  Since they are hard to detect, scientists do not have a very accurate assay of their frequency in the universe.  The question bears somewhat on our understanding of the universe–since a great deal of matter is  not accounted for.

An artist's conception of a brown dwarf seem from a closely orbiting planet

An artist’s conception of a brown dwarf seem from a closely orbiting planet

My mind keeps returning to the fact that some brown dwarfs have planetary systems.  Imagine these melancholic twilight ice worlds forever orbiting a dim glow which will never blaze into a true sun.   It is a melancholy picture, but not without a certain beauty.

A Brown Dwarf with Planet and Moon (painting by Lynette Cook from fineartamerica.com)

A Brown Dwarf with Planet and Moon (painting by Lynette Cook from fineartamerica.com)

An astronomy story has made big news headlines this week.  Usually most people are not unduly interested in the happenings in the heavens (either because such events are difficult to comprehend, or because they are regarded as remote to human interests), however this story does directly involve matters which humans take great interest in. gold-bar Scientists and theorists working for the Harvard-Smithsonian Center for Astrophysicists have announced a spectacular new theory concerning the origin of gold (and other heavy elements like platinum and uranium): the cosmologists believe that the heaviest natural elements are created when two neutron stars collide or when a neutron star collides with a black hole (here is an easy summary of neutron stars, extremely tiny supernova remnants with a mass greater than the sun).  Elements as complicated as iron are manufactured by normal stars in the course of their lifetime, however the creation of heavier elements is more mysterious.  Until now, chemists and physicists had imagined that gold, platinum, uranium, and what have you, come from supernovae—however computer models of various types of supernova events did not supporting that conjecture. The scientists at the Harvard-Smithsonian Center for Astrophysicists based their hypothesis partly on the massive gamma radiation burst detected on June 3rd, 2013 from 3.9 billion light years away in a galaxy located in the constellation Leo.  Gamma ray bursts tend to be associated with hypernovae/supernovae caused by the collapse of super-giant stars, but the June 3rd burst was different.  In certain rare circumstances, two neutron stars are in a binary system together.  Over time, the orbits decay and the stars come together in a cataclysmic event which releases energy tantamount to that of a supernova.    Based on the unusual exotic energy signatures of the June 3rd gamma ray burst,  it seems that scientists caught a rare peek at such an event.

Neutron Star Collision

Neutron Star Collision

I will confess that I am having trouble imagining two objects the size of small cities (yet each with a mass greater than the sun) slamming into each other at astronomical speeds.  Apparently such events only happen every 100,000 years or so in a galaxy the size of the Milky Way.  When the neutron stars come together, a black hole is ripped in the fabric of spacetime.  Huge parts of the neutron stars fall into the black hole and vanish from this universe, but other portions of the neutron stars (which, as the name hints, are made up largely of neutrons) are jettisoned into space.  Edo Berger, one of the astrophysicists who authored the new theory described the process with an earthy metaphor, saying, “several exciting things happen very quickly…. Most of the material collapses to form a black hole. Some of it is spewed into space. That material is rich in neutrons, which drives the formation of heavier and heavier elements, the way mud piles up on an off-road vehicle.” neutcol The gold, platinum, and heavy elements are created in astonishing mass (like many earths made entirely of gold).  The elements are diffused through the cosmos and become part of newly forming star systems. Gold is strange stuff anyway.  The gold present on Earth during its nebular formation is believed to have sunk deep into the center of planet’s molten core where it is inaccessible.  All the gold that rappers and kings wear (and that Ron Paul and draugers hoard) first began falling to Earth 200 million years after the planet’s final formation on asteroids.  The great gold strikes are well named: gold on the surface of Earth is there because of meteor strikes (although billions of years of geology have buried and twisted and hidden these cosmic remnants).

Yeehaw! There's asteroid fragments!

Yeehaw! There’s asteroid fragments!

Dr. Brian May, astrophysicist, CBE

Dr. Brian May, astrophysicist, CBE

Brian May is an astrophysicist who pursued a career in music. He is the guitarist for the rock band Queen and he is more famous for writing “Fat Bottomed Girls”, “We Will Rock You”, & “Who Wants to Live Forever” than for anything he wrote while obtaining his Astrophysics degrees.  Brian was popularizing Galaxy Zoo on his blog (Galaxy Zoo is an online project which seeks public help in classifying vast numbers of galaxies.  A Dutch fan, Hanny van Arkel (a schoolteacher by trade), became interested in the project and started working on the site when she spotted a huge weird glowing green thing below spiral galaxy IC 2497.  She presented her findings to professional astronomers, who were also perplexed by the ghostly shape.  They duly named the object in her honor “Hanny’s Voorwerp” (which is Dutch for “Hanny’s thing”).

Hanny's Voorwerp and Galaxy IC2497 (Hubble Space Telescope)

Hanny’s Voorwerp and Galaxy IC2497 (Hubble Space Telescope)

So what is Hanny’s Voorwerp? The leading theory is that the supermassive black hole in the center of IC 2497 created huge jets of energy and gas as it (messily) devoured great masses of matter at the center of that galaxy.  These esoteric plumes interacted with an unrelated stream of gaseous matter hundreds of thousands of light years long (which is longer than our galaxy).  The thin clouds of glass then fluoresced like a krypton sign or a Scooby-Doo ghost.

Hanny Van Arkel

Hanny Van Arkel

Thanks Brian May and Hanny! This is one fancy voorwerp.

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