The Big Freeze

September 10, 2015

The Robert Frost poem, Fire and Ice,[1] has the opening lines, "Some people say the world will end in fire, Some say in ice." As referenced in Wikipedia, astronomer Harlow Shapley (1885-1972) thought that he had inspired this poem. A year before the poem was published, Frost asked Shapley how the world would end. Shapley said that the Sun would either die out ("ice"), or it would explode ("fire").

Fire & Ice. Sunset at Woodbine Beach, Toronto, Canada, after a rainstorm. (Photo by Benson Kua, via Wikimedia Commons.)

Whether the universe, itself, has its own fire-or-ice end point was a question debated in the early part of the 20th century. After universal expansion was discovered, some cosmologies claimed that the universe would continue to expand ("ice"), while others thought that the expansion would eventually reverse itself, leading to what's poetically described as the Big Crunch ("fire").

The Big Crunch would be followed by another Big Bang, and the universe would be reborn. This is the cosmology in the Futurama episode, The Late Philip J. Fry (Season 6, episode 7). In that episode, the evolution of the reborn universe is precisely the same as the old one, within a ten foot error. Recent observations indicate that the universal expansion is accelerating, so it looks as if we are headed towards a Big Freeze.

A huge international team of nearly a hundred astronomers from 33 institutions has just published a thorough analysis of how fast the universe is winding down.[2-5] The team was led by Simon P. Driver, a professor of astrophysics at the University of St. Andrews School of Physics & Astronomy. They precisely measured the energy generation of more than 200,000 galaxies to create a comprehensive assessment of the energy output of the universe in our region of space. They found that the energy production of these galaxies has declined by 50% in the past two billion years.

This study was part of the Galaxy And Mass Assembly (GAMA) project using many of the world's telescopes to survey galaxies at many wavelengths.[3-4] Says Prof. Driver, who presented the team's findings from far ultraviolet to far infrared at the International Astronomical Union XXIX General Assembly (Honolulu, Hawaii, August 10, 2015),

"We used as many space and ground-based telescopes as we could get our hands on to measure the energy output of over 200,000 galaxies across as broad a wavelength range as possible."[3-4]

The current dataset, which includes measurements of the energy output of each galaxy at 21 wavelengths, was obtained by the following ground-based and space telescopes (in order of increasing wavelength): GALEX, SDSS, VST, AAT, VISTA, UKIRT, WISE, and Herschel.[3-4]

A galaxy from the Galaxy And Mass Assembly (GAMA) project observed at different wavelengths from the far ultraviolet to the far infrared. (Simplified ICRAR / GAMA image.)

The two principle sources of energy in the universe are the nuclear fusion in stars, and the gravitational energy from the infall of matter near the black holes at galactic centers. The black holes create hot discs of matter around the galactic nuclei. Dust clouds create longer wavelength radiation by absorbing and re-radiating energy.[3-4] The object of the GAMA study is the mapping and modeling of all of these energy sources in a large volume of space representative of present and past times.[3-4]

Typical energy spectrum of a galaxy from the far ultraviolet (left) to the far infrared (right). (Source data: ICRAR / GAMA image.)

As Driver explains,

"While most of the energy sloshing around in the Universe arose in the aftermath of the Big Bang, additional energy is constantly being generated by stars as they fuse elements like hydrogen and helium together... This new energy is either absorbed by dust as it travels through the host galaxy, or escapes into intergalactic space and travels until it hits something, such as another star, a planet, or, very occasionally, a telescope mirror."[3-5]

It's been known since the late 1990s that the universe is winding down, but the GAMA survey is the first attempt to detail the decline. The data, says Driver, show that "the universe has basically sat down on the sofa, pulled up a blanket and is about to nod off for an eternal doze."[3-5]

GAMA's future plan is to add the radio spectrum to its survey, getting data from other observatories, including the Square Kilometre Array (SKA). The SKA will be the world's largest radio telescope once it's built in Australia and South Africa.[3-4] A "fly-through" of objects in the GAMA survey is available at ref. 6.[6]

A galaxy from the GAMA survey observed at different wavelengths by different telescopes. (Portions of an ICRAR / GAMA image.)

References:

1. Robert Frost, "Fire and Ice," Harper's Magazine, vol. 142, p. 67 (Via Google Books).
2. Simon P. Driver, et al., "Galaxy And Mass Assembly (GAMA): Panchromatic Data Release (far-UV|far-IR) and the low-z energy budget." Monthly Notices of the Royal Astronomical Society (To Appear). Also at http://www.simondriver.org/mwavev02.pdf.
3. Charting the Slow Death of the Universe - GAMA survey releases first data at IAU General Assembly, European Space Agency Press Release eso1533, August 10, 2015.
4. Charting the Slow Death of the Universe - GAMA survey releases first data at IAU XXIX General Assembly, International Astronomical Union Press Release iau1509, August 10, 2015.
5. Scientists measure Slow Death of the Universe, International Centre for Radio Astronomy Research (ICRAR) Press Release, August 11, 2015
6. A fly-through of objects in the GAMA survey by Will Parr, Dr. Mark Swinbank and Dr. Peder Norberg (Durham University) using data from the SDSS and the GAMA surveys. Music composed and created by Holly Broadbent.