The intergalactic medium in the young universe

Sep 30, 2013
A picture of the 6.5-meter MMT primary mirror. The MMT was used to study the afterglow of a gamma-ray burst, and to measure for the first time the presence of neutral material in clouds of gas in the early universe. Credit: MMT Observatory

(Phys.org) —In its earliest years, the universe was so hot that electrons and protons could not bind together in neutral atoms: all of the gas in the cosmos was ionized. Then, after 380,000 years of expansion, the universe cooled enough for hydrogen atoms and some helium (about 25%) to form. Much later in cosmic history—the precise dating is an active area of current research but perhaps after a few hundred million years—the first generation of stars emerged from the vast expanses of atomic gas, and these stars emitted enough strong ultraviolet light to re-ionize the neutral hydrogen in their vicinity. As the universe continued to expand and evolve, newer generations of stars continued to re-ionize the hydrogen until at some time most gas between galaxies (the intergalactic medium) was ionized once again. The epoch of re-ionization is an important diagnostic tool because it traces when the first generations of stars were being made, and it provides crucial details about the early evolution of the universe.

Searching for signs of ionized hydrogen from more than ten billions years ago is not a simple task. One method takes advantage of the stupendous luminosities of distant quasars, galaxies dominated by supermassive black holes actively accreting material and shining brightly. If clouds of neutral hydrogen lie between us and a quasar, astronomers can detect them because they absorb the quasar's light at characteristic wavelengths. Indeed, the first detection of these clouds was made in the 1960's (although from quasars that are relatively close to us).

CfA astronomers Ryan Chornock, Edo Berger, Ragnhild Lunnan, Maria Drout, Wen-Fai Fong, and Tanmoy Laskar, and their colleagues have pioneered a new technique to study reionization: using the light emitted in the afterglow of a gamma-ray burst (GRB) to probe the intervening gas. GRBs are the brightest events in the known universe, and result from especially spectacular supernovae, the deaths of massive stars. They occur about once a day, randomly, around the sky, with most of them shining only for a few minutes—but, because they are so bright, they can be seen even when they are very, very far away. After the blasts dies away, a faint afterglow remains, and when a GRB is spotted in time, follow-up observations of its afterglow can be made. In this new study, the astronomers were able to use the afterglow of a GRB to probe the neutral intergalactic medium.

The GRB in this study went off last June 6 and the blast lasted for 277 seconds; it was discovered with NASA's Swift satellite. The scientists began observing its afterglow six hours and fifty nine minutes later using the joint Smithsonian-Arizona MMT Observatory. They discovered from the optical spectrum (that is, from its redshift and corresponding distance) that the burst went off when the was about 970 million years old. They also found in the spectrum absorption features signaling the presence of some distant clouds of neutral gas between us and the burst. The results are significant because they mark the first time that the afterglow from GRBs has been used to probe the gas at cosmological distances, and support earlier conclusions that by this period in the evolution of the cosmos most (but not all) material had been ionized.

Explore further: Is the universe finite or infinite?

More information: "GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar Medium in a Star-Forming Galaxy in the First Gyr After the Big Bang," Ryan Chornock, Edo Berger, Derek B. Fox, Ragnhild Lunnan, Maria R. Drout, Wen-fai Fong, Tanmoy Laskar, and Katherine C. Roth, ApJ 774, 26, 2013.

add to favorites email to friend print save as pdf

Related Stories

Explosion illuminates invisible galaxy in the dark ages

Aug 06, 2013

(Phys.org) —More than 12 billion years ago a star exploded, ripping itself apart and blasting its remains outward in twin jets at nearly the speed of light. At its death it glowed so brightly that it outshone ...

Earth's gold came from colliding dead stars

Jul 17, 2013

We value gold for many reasons: its beauty, its usefulness as jewelry, and its rarity. Gold is rare on Earth in part because it's also rare in the universe. Unlike elements like carbon or iron, it cannot ...

Possibly the most distant object known

Jul 18, 2011

The most distant objects in the universe are also the oldest -- or at least that is how they appear to us, because their light has had to travel for billions of years to get here. They are also extraordinarily ...

Recommended for you

Is the universe finite or infinite?

Mar 27, 2015

Two possiblities exist: either the Universe is finite and has a size, or it's infinite and goes on forever. Both possibilities have mind-bending implications.

'Teapot' nova begins to wane

Mar 27, 2015

A star, or nova, has appeared in the constellation of Sagittarius and, even though it is now waning, it is still bright enough to be visible in the sky over Perth through binoculars or a telescope.

Dark matter is darker than once thought

Mar 27, 2015

This panel of images represents a study of 72 colliding galaxy clusters conducted by a team of astronomers using NASA's Chandra X-ray Observatory and Hubble Space Telescope. The research sets new limits on ...

Galaxy clusters collide—dark matter still a mystery

Mar 26, 2015

When galaxy clusters collide, their dark matters pass through each other, with very little interaction. Deepening the mystery, a study by scientists at EPFL and the University of Edinburgh challenges the ...

Using 19th century technology to time travel to the stars

Mar 26, 2015

In the late 19th century, astronomers developed the technique of capturing telescopic images of stars and galaxies on glass photographic plates. This allowed them to study the night sky in detail. Over 500,000 ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Fleetfoot
5 / 5 (3) Sep 30, 2013
cantdrive85
1 / 5 (8) Sep 30, 2013
Maybe they should try to figure out the characteristics of this medium now before speculating on this medium in some hypothetical era in the past.
Torbjorn_Larsson_OM
5 / 5 (7) Sep 30, 2013
Antiscience trolling is always negative, even when the observations supports the theories or vice versa. Naturally as they can't supply alternatives by definition - but the whining is also laughably stupid. LOL!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.