Crisis in the cosmos? Galaxy-formation theory is in peril.
Imagine peering into a nursery and seeing, among the cooing babies, a few that look like grown men. That's the startling star·tle
v. star·tled, star·tling, star·tles
1. To cause to make a quick involuntary movement or start.
2. To alarm, frighten, or surprise suddenly. See Synonyms at frighten. situation that astronomers have stumbled upon as they've looked deep into space and thus back to a time when newborn galaxies filled the cosmos. Some of these babies have turned out to be nearly as massive as the Milky Way Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky. and other galactic geezers that have taken billions of years to form. Despite being only about 800 million years old, some of the infants are chock-full of old stars.
These chunky babies may be pointing to a cosmic crisis. They don't seem to fit the leading theory of galaxy formation, which cosmologists have relied on for more than 2 decades to explain an assortment of puzzling features of the universe.
The theory posits that a pervasive, slow-moving, invisible type of matter vastly outweighs the observable matter in the universe. Under the gravitational grav·i·ta·tion
a. The natural phenomenon of attraction between physical objects with mass or energy.
b. The act or process of moving under the influence of this attraction.
2. influence of this unseen material, known as cold dark matter (SN: 4/23/05, p. 264), galaxies start out as small, starry star·ry
adj. star·ri·er, star·ri·est
1. Marked or set with stars or starlike objects.
2. Shining or glittering like stars.
3. Shaped like a star.
4. Illuminated by stars; starlit. fragments that merge to become much bigger objects. That's usually a gradual process, according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. the theory.
The new findings raise the question: Did the universe have enough time during its first 800 million years for infant galaxies to have merged into mature-looking behemoths?
The theory can accommodate a few rare instances of such precocious growth by assuming that the jumbo galaxies reside in a few regions that have an unusually high density of dark matter. There, gravity would have pulled together objects faster than usual, accelerating galaxy growth.
But over the past 18 months, several teams have found so many massive galaxies from this early epoch that the theory is being stretched to its breaking point, several astronomers say.
"Our expectation is that [in the cold dark matter model] when you look back in time, it should be hard to see very massive structures because most galaxies at that early time in the universe are expected to be small," says astronomer Michael Rowan-Robinson Michael Rowan-Robinson is an astronomer and astrophysicist. He is Professor of Astrophysics and head of the Astronomy and Astrophysics Department at Imperial College London. From 1981 to 1982, he gave public lectures as professor of astronomy at Gresham College. of the Imperial College of Science, Technology and Medicine (education) Imperial College of Science, Technology and Medicine - (IC, ICST&M) One of the colleges of London University. The Department of Computing is the home of FOLDOC.
IC Home. in London. "It would be worrying if this kind of [massive] galaxy is common" at early times.
If too many early, massive galaxies show up, "we might not have the right galaxy-formation scenario," says Bahram Mobasher of the Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST; in orbit since 1990) and for the James Webb Space Telescope (JWST; scheduled to be launched in 2013). in Baltimore.
Even if the theory of cold dark matter survives this onslaught, the new observations of big galaxies in the most ancient of times have important implications. The findings suggest that the earliest galaxies formed stars in a great hurry, much more rapidly than galaxies that were born even a billion years later did. What's more, that first generation of stars might have been rife with heavyweights much more massive, on average, than stars from any later epoch.
BIG BABIES? Over the past few years, researchers have detected several galaxies that were surprisingly massive, given that their measured distance puts them in the early universe (SN: 3/1/03, p. 139). Two of the galaxies, recently round by Andrew Bunker of the University of Exeter in England and his colleagues, are less than a billion years old, which is less than 5 percent of the age of the universe.
Despite their youth, these galaxies contain stars that formed at least 100 million years earlier in time. Furthermore, the galaxies are at least 20 percent as massive as todays typical bright galaxy, which took some 12 billion years to pack on that material.
The team reports several of its findings in an upcoming Monthly Notices of the Royal Astronomical Society Monthly Notices of the Royal Astronomical Society (MNRAS) is one of the world's leading scientific journals in astronomy and astrophysics. It has been in continuous existence since 1827 and publishes peer-reviewed letters and papers reporting original research in relevant .
In a report on Sept. 27, Mobasher and his colleagues describe what appears to be an even more outlandish result. They have evidence of a true whopper Whopper - WarGames of a galaxy--perhaps the most massive ever detected from the early universe. Observations taken at several visible-light and infrared wavelengths suggest that it's likely to be one of the earliest galaxies ever found. It appears to reside 13 billion light-years from Earth. So, the light now reaching our planet left the galaxy when the cosmos was about 800 million years old.
Mobasher's group estimates that the galaxy is six times as massive as the Milky Way. Moreover, the reddish tinge of the galaxy's stars indicates that they're quite mature and must have formed about 200 hundred million years farther back in time.
Bunker's team found a similarly old, red population of stars in the young galaxies they've detected.
In contrast, most galaxies observed at such an early epoch are aglow with the blue light emitted by clumps of hot, newborn stars, notes Richard Ellis There are several prominent people named Richard Ellis, including
v. teemed, teem·ing, teems
1. To be full of things; abound or swarm: A drop of water teems with microorganisms.
2. with new stars, says Ellis.
The finding affirms that "there probably was a very luminous early period of [stellar] activity that we haven't yet witnessed," he says.
"That's terrific news for those of us who are working on the James Webb Space Telescope This article or section documents a scheduled or expected spaceflight. Details may change as the launch date approaches or more information becomes available. [the proposed successor to the Hubble Space Telescope Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe. ] and future ground-based telescopes" that will be capable of looking farther back in time, he adds.
However, because Mobasher's team hasn't obtained a spectrum of the galaxy--the only sure way to measure its distance--the researchers can't be positive that the object is as remote and ancient as their images suggest.
Although the team's models deem it unlikely, Mobasher says that it's possible that instead of lying near the edge of the observable universe--and therefore residing far back in time--the galaxy is much closer and looks red merely because it's heavily shrouded in dust.
SEEKING THE YOUNG BUT OLD To find old-looking young galaxies, astronomers combine the sharp eye of the Hubble Space Telescope, which can image faint galaxies in visible and near-infrared light, with the much-longer-wavelength infrared sensitivity of the Spitzer Space Telescope Spitzer Space Telescope: see infrared astronomy; observatory, orbiting. .
The Hubble images were recorded as part of the Ultra Deep Field, the deepest survey of the heavens ever conducted in visible light. Between September 2003 and January 2004, Hubble stared at a patch of sky about one-tenth the diameter of the full moon for a total of 11 days, recording distant galaxies in unprecedented detail (SN: 05/15/04, p. 309).
A distant galaxy typically shows up at about the same brightness in near-infrared and visible-red wavelengths but vanishes at shorter wavelengths. That's because clouds of hydrogen gas absorb far-ultraviolet light, and the most distant galaxies have the largest amount of hydrogen gas between them and Earth (SN: 2/24/96, p. 120). The expansion of the universe shifts light from the remote galaxies to longer wavelengths, so the galaxies drop out of sight not in the far-ultraviolet but at longer wavelengths--blue visible light.
Once astronomers identify a galaxy as a distant dropout (1) On magnetic media, a bit that has lost its strength due to a surface defect or recording malfunction. If the bit is in an audio or video file, it might be detected by the error correction circuitry and either corrected or not, but if not, it is often not noticed by the human , they turn to the infrared Spitzer telescope to estimate the mass and age of its constituent stars. An infrared telescope infrared telescope
A telescope, similar in operation to an optical telescope, that is designed to detect infrared radiation. Because infrared radiation is emitted by warm objects, infrared telescopes need to be shielded from local heat sources, as by is a prerequisite because the majority of stars in any galaxy glow strongest in the infrared. The infrared-brightest stars are also the oldest ones. Therefore, the brighter a galaxy appears in Spitzer images, the older its stars.
With Spitzer, notes Bunker, "we can attempt to age-date the stars." The observations indicate that some of the youngest galaxies in the universe are prematurely old. The stars in these infrared-bright distant galaxies formed a mere half-billion years after the Big Bang big bang
Model of the origin of the universe, which holds that it emerged from a state of extremely high temperature and density in an explosive expansion 10 billion–15 billion years ago. .
SIFTING THROUGH Nonetheless, theorists who study galaxy formation maintain that the cold dark matter model isn't yet in peril. Simon White of the Max Planck Institute for Astrophysics The Max Planck Institute for Astrophysics is a Max Planck Institute, located in Garching, near Munich, Bavaria, Germany. It was founded as Max Planck Institute for Physics and Astrophysics in Garching, Germany, says that the would-be spoilers have yet to demonstrate that massive galaxies in the early universe are common enough to pose a problem.
Mobasher told Science News that his team is currently studying several other galaxies within the Ultra Deep Field data that might be nearly as massive and as distant as the galaxy that his team has just announced.
"There could be a problem with the theory," says theorist Avi Loeb of the Harvard-Smithsonian Center for Astrophysics The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. It consists of the Harvard College Observatory and the Smithsonian Astrophysical Observatory. The Center is located at 60 Garden Street. in Cambridge, Mass. "Any additional examples of [young] massive galaxies would be very useful for theorists attempting to figure out the implication."
If cold dark matter does run into trouble, the theory won't be salvaged with just a small bit of tinkering, Loeb warns. It's possible that the universe is populated by a type of dark matter different from that which cosmologists have considered most plausible, he adds.
Another idea, Loeb notes, harks back to the notion that chance, microscopic fluctuations in the density of the primordial cosmic soup gave birth to galaxies. Perhaps, he says, those fluctuations aren't uniformly distributed but are skewed skewed
curve of a usually unimodal distribution with one tail drawn out more than the other and the median will lie above or below the mean.
skewed Epidemiology adjective Referring to an asymmetrical distribution of a population or of data to make the formation of rare, massive galaxies more likely than researchers had supposed.
If the galaxy found by Mobasher's team turns out to be too small to challenge current theory, it may nonetheless reveal the nature of the first generation of stars in the universe. The finding would add to the evidence that stars, not the black hole--powered beacons known as quasars Proper naming of quasars are by Catalogue Entry, Qxxxx±yy using B1950 coordinates, or QSO Jxxxx±yyyy using J2000 coordinates.
This page lists quasars.
To gauge the galaxy's mass, Mobasher's team observed the brightness at several infrared wavelengths. The infrared glow comes from the galaxy's predominant stellar population--low-mass stars. Using the ratio of low-mass to high-mass stars measured in galaxies today, the team estimated the young galaxy's total stellar mass.
When researchers make such estimates, they assume that the ratio has remained the same throughout cosmic history. If that ratio was lower in the past, the galaxy would weigh less than Mobasher's team has estimated. It would also indicate, as some simulations suggest, that stars of the first generation were heftier than those in later generations.
The prospect of determining the nature of the first stars is thrilling, says Ellis, because their characteristics will reveal whether they were critical for ending the era known as the cosmic dark ages.
This dark era began some 300,000 years after the birth of the universe, when the radiation left over from the Big Bang streamed freely into space and faded.
The dark ages continued even as the first stars and quasars emerged from the murk murk also mirk
Partial or total darkness; gloom.
Partially or totally dark; gloomy.
[Middle English mirke, from Old Norse myrkr because their light was quenched quench
tr.v. quenched, quench·ing, quench·es
1. To put out (a fire, for example); extinguish.
2. To suppress; squelch: by hydrogen atoms. Only when those first objects generated enough ultra-violet light to break these atoms apart into protons and electrons could starlight flood the cosmos.
Cosmologists aren't sure whether quasars, stars, or both first lit up the universe. But the heftier the first generation of stars, the more important they would have been in switching on the cosmos. That's because the more massive a star is, the more ultraviolet light Ultraviolet light
A portion of the light spectrum not visible to the eye. Two bands of the UV spectrum, UVA and UVB, are used to treat psoriasis and other skin diseases. it can produce, breaking apart atoms and lighting the cosmos.
Indirectly, then, the galaxy discovered by Mobasher's group may be unusually illuminating. It might point to the group of stars that generated the cosmic dawn.