Distant quasar exposes a hungry galaxy’s snacking habits

This artist’s impression shows a distant galaxy that formed just two billion years after the Big Bang, in the process of pulling in cool gas (shown in orange) from its surroundings. Astronomers have been able to find out a lot about the object by taking advantage of a rare alignment of the galaxy and more distant quasar (bright object left of the central galaxy). Credit: L. Calcada/ESA/AOES Medialab

Like a guy munching chips in front of the TV, galaxies increase their girth by snacking on what they find handy. That’s the finding of a multinational team of astronomers in a recently published paper on the eating habits of galaxies.

Using the European Southern Observatory’s Very Large Telescope, astronomers took advantage of a rare alignment of a distant quasar and the foreground galaxy HE 2243-60 in the southern constellation of Tucana the Toucan. A quasar or ‘quasi-stellar radio source’ looks like a faint star but up close what appears as starlight is really matter heated to incandescence as it gets sucked into a supermassive black hole at the center of remote galaxies. Quasars send out radiation of many flavors including visible light and radio waves.

The quasar 3C273 photographed with the Hubble Space Telescope looks like a star and far outshining its host galaxy. When the quasar is blocked with a special occulting disk, the galaxy is much easier to see during a long time exposure (right). Credit: NASA/ESA

More than 200,000 quasars are known and most are extremely distant, upwards of 3 billion light years. Though they appear faint, they’re the most luminous objects in the universe. The brightest, 3C273 in Virgo, shines at just 12th magnitude and looks identical to a star.

Supernovae explosions return materials including gases enriched with heavier elements like nickel, gold and iron to space where they can be recycled into new stars. Credit: ESO

Like everything else in the universe, galaxies are born from great clouds of gas and dust, which they quickly use up manufacturing stars and planets. While some of the matter is recycled into new stars through supernovae and the huff-and-puff of ageing sun-like stars, galaxies need more food to maintain their sparkle.

How do they do it? Gravitational muster. Galaxies pull in cool gas from their surroundings which circles about them like water going down your bathtub drain. Once the gas enters the celestial pinwheel it’s ultimately fashioned into stars through self-gravity, providing twinkling tiki lamps to light the galactic night.

Artist’s impression shows ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun. This quasar is the brightest object discovered so far in the early universe. Credit: ESO /R. Kornmesser

Astronomers have found evidence of galaxies’ gas guzzling habits before, but this time the laser-like beam of the remote quasar QSO J2246-6015 passing through the foreground galaxy allowed astronomers to probe the composition and motion of the infalling gas in unprecedented detail.

The gas clouds absorb narrow segments of the quasar’s beam leaving a pattern of distinctive dark lines – fingerprints as it were – in its light spectrum. Every element and molecule has it own set of fingerprints. Find and measure them and you can determine the composition of everything from stars to asteroids to succulent gas clouds.

“In this case we were lucky that the quasar happened to be in just the right place for its light to pass through the infalling gas. The next generation of extremely large telescopes will enable studies with multiple sight lines per galaxy and provide a much more complete view,” concludes co-author Crystal Martin of University of California Santa Barbara.

Now back to eating more chips.

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

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