Infant galaxies -- small and hyperactive

Feb 05, 2009
False-color image of the galaxy J1148+5251, based on observations from the Very Large Array in New Mexico. Credit: Image: NRAO/AUI/NSF

Galaxies, including our own Milky Way, consist of hundreds of billions of stars. How did such gigantic galactic systems come into being? Did a central region with stars first form then with time grow? Or did the stars form at the same time throughout the entire galaxy? An international team led by researchers from the Max Planck Institute for Astronomy is now much closer to being able to answer these questions.

The researchers studied one of the most distant known galaxies, a so-called quasar with the designation J1148+5251. Light from this galaxy takes 12.8 billion years to reach Earth; in turn, astronomical observations show the galaxy as it appeared 12.8 billion years ago, providing a glimpse of the very early stages of galactic evolution, less than a billion years after the Big Bang.

With the IRAM Interferometer, a German-French-Spanish radio telescope, the researchers were able to obtain images of a very special kind: they recorded the infrared radiation emitted by J1148+5251 at a specific frequency associated with ionized carbon atoms, which is a reliable indicator of ongoing star formation.

The level of star-forming activity in the Orion-KL region (marked by the rectangle) in the Orion nebula is comparable to that of the central region of J1148+5251, but confined to a much smaller volume of space. Credit: NASA, ESA, Robberto (STScI/ESA), Orion Treasury Project Team

The resulting images show sufficient detail to allow, for the first time, the measurement of the size of a very early star-forming region. With this information, the researchers were able to conclude that, at that time, stars were forming in the core region of J1148+5251 at record rates - any faster and star formation would have been in conflict with the laws of physics.

"This galaxy's rate of star production is simply astonishing," says the article's lead author, Fabian Walter of the Max Planck Institute for Astronomy. "Every year, this galaxy's central region produces new stars with the combined mass of more than a thousand suns." By contrast, the rate of star formation within our own galaxy, the Milky Way, is roughly one solar mass per year.

Close to the physical limit

It has been known for some time that young galaxies can produce impressive amounts of new stars, but overall activity is only part of the picture. Without knowing the star-forming region's size, it is impossible to compare star formation in early galaxies with theoretical models, or with star-forming regions in our own galaxy.

With a diameter of a mere 4000 light-years (by comparison: the Milky Way galaxy's diameter amounts to 100,000 light-years), the star-forming core of J1148+5251 is extremely productive. In fact, it is close to the limits imposed by physical law. Stars are formed when cosmic clouds of gas and dust collapse under their own gravity. As the clouds collapse, temperatures rise, and internal pressure starts to build. Once that pressure has reached certain levels, all further collapse is brought to a halt, and no additional stars can form. The result is an upper limit on how many stars can form in a given volume of space in a given period of time.

Remarkably, the star-forming core of J1148+5251 reaches this absolute limit. This extreme level of activity can be found in parts of our own galaxy, but only on much smaller scales. For example, there is a region within the Orion nebula (Fig. 2) that is just as active as what we have observed. Fabian Walter: "But in J1148+5251, we are dealing with what amounts to a hundred million of these smaller regions combined!" Earlier observations of different galaxies had suggested an upper limit that amounts to a tenth of the value now observed in J1148+5251.

Growth from within

The compact star-forming region of J1148+5251 provides a highly interesting data point for researchers modelling the evolution of young galaxies. Going by this example, galaxies grow from within: in the early stages of star formation, there is a core region in which stars form very quickly. Presumably, such core regions grow over time, mainly as a result of collisions and mergers between galaxies, resulting in the significantly larger star-filled volume of mature galaxies.

The key to these results is one novel measurement: the first resolved image of an extremely distant quasar's star-forming central region, clearly showing the region's apparent diameter, and thus its size. This measurement is quite a challenge in itself. At a distance of almost 13 billion light-years (corresponding to a red-shift z = 6.42), the star-forming region, with its diameter of 4000 light-years, has an angular diameter of 0.27 seconds of arc - the size of a one euro coin, viewed at a distance of roughly 18 kilometres (or a pound coin, viewed at a distance of roughly 11 miles).

There is one further handicap: the observations rely on electromagnetic radiation with a characteristic wavelength, which is associated with ionized carbon atoms. At this wavelength, the star-forming regions of J1148+5251 outshine even the quasar's ultra-bright core. Due to the fact that the universe is expanding, the radiation is shifted towards longer wavelengths as it travels towards Earth ("cosmological redshift"), reaching our planet in the form of radio waves with a wavelength of about one millimetre. But, owing to the general nature of waves, it is more than a thousand times more difficult to resolve minute details at a wavelength of one millimetre, compared with visible light.

Observations at the required wavelength and level of detail became possible only as recently as 2006, thanks to an upgrade of the IRAM Interferometer, a compound radio telescope on the Plateau de Bure in the French Alps.

Future telescopes

Use of the characteristic radiation of ionized carbon to detect and create images of star-forming regions of extremely distant astronomical objects had been suggested some time ago. A significant portion of the observational program for ALMA, a compound radio telescope currently under construction in Northern Chile, relies on this observational approach. But up until the measurements of Fabian Walter and his colleagues, this technique had not been demonstrated in practice. Quoting Walter: "The early stages of galaxy evolution, roughly a billion years after the Big Bang, will be a major area of study for years to come. Our measurements open up a new window on star-forming regions in very young galaxies".

On the web: The IRAM telescope - www.iram.fr/

Paper: Fabian Walter, Dominik Riechers, Pierre Cox, Roberto Neri, Chris Carilli, Frank Bertoldi, Axel Weiss, Roberto Maiolino, A kiloparsec-scale hyper-starburst in a quasar host less than 1 gigayear after the Big Bang, Nature, February 5th, 2009

Source: Max-Planck-Gesellschaft

Explore further: Next-generation Thirty Meter Telescope begins construction in Hawaii

add to favorites email to friend print save as pdf

Related Stories

First in-situ images of void collapse in explosives

57 minutes ago

While creating the first-ever images of explosives using an x-ray free electron laser in California, Los Alamos researchers and collaborators demonstrated a crucial diagnostic for studying how voids affect ...

NASA maps Typhoon Matmo's Taiwan deluge

1 hour ago

When Typhoon Matmo crossed over the island nation of Taiwan it left tremendous amounts of rainfall in its wake. NASA used data from the TRMM satellite to calculate just how much rain fell over the nation.

Recommended for you

Comet Jacques makes a 'questionable' appearance

Jul 28, 2014

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

Image: Our flocculent neighbour, the spiral galaxy M33

Jul 28, 2014

The spiral galaxy M33, also known as the Triangulum Galaxy, is one of our closest cosmic neighbours, just three million light-years away. Home to some forty billion stars, it is the third largest in the ...

Image: Chandra's view of the Tycho Supernova remnant

Jul 25, 2014

More than four centuries after Danish astronomer Tycho Brahe first observed the supernova that bears his name, the supernova remnant it created is now a bright source of X-rays. The supersonic expansion of ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

MrGrynch
1.4 / 5 (5) Feb 05, 2009
"Light from this galaxy takes 12.8 billion years to reach Earth"

Really? How do they know this? From red-shift of light? I hope not since red-shift is an unreliable indicator of distance (or recessional) velocity as pointed out by Dr. Halton Arp in his catalog of galaxies. He believes red-shift to be largely intrinsic, and is more indicative of age, rather than distance and/or recessional velocity. Red-shift occurs in discrete values and progresses quite predictably from the active galactic nuclei which spawn infant galaxies on either side of its central axis.

"Due to the fact that the universe is expanding"

Really? how is this determined? Red-shift?? c'mon! See above.

The universe is not expanding, at least not universally (no pun intended). Once the fallacy of red-shift as a reliable measure of distance or recessional velocity is embraced, the universe takes on a completely different form, and we'll be left to answer the questions of it all once again.
LuckyBrandon
3 / 5 (4) Feb 05, 2009
to deny the expansion of the universe is to deny that a bubble expands...simply idiotic
yep
1 / 5 (2) Feb 24, 2009
Idiotic? Does the universe have an edge? The expanding universe theory "big bang" was proven false half a century ago.
http://www.holosc...bqx15w21&keywords=expanding univers#dest