Discovery of ‘Baby Galaxy’ a Clever Feat

Using a clever technique that pushed two of the world’s most powerful telescopes to their limits, a team of scientists has discovered a “baby galaxy” so small, faint and distant that it may be one of the long sought-after building blocks of modern galaxies.

To find their galactic infant, the astronomers used a phenomenon predicted by Albert Einstein in the general theory of relativity--employing a massive group of galaxies, themselves, as an extra lens.

Most astronomers believe today’s massive spiral and elliptical galaxies emerged from much smaller building blocks made up of clusters of stars. But astronomers have had a hard time seeing the galactic birthing process: Even the oldest known galaxies look similar to modern, mature galaxies, such as our own Milky Way.

“It’s like we were trying to peer into the delivery room of the hospital and all we saw were adults,” said Bruce Margon, associate director for science at the Space Telescope Science Institute in Baltimore.

Not anymore. The so-called baby galaxy is a scant 500 light-years across--nothing compared to the 100,000-light-year girth of our Milky Way, an average-sized galaxy.

It is estimated to contain just a few million times as much mass as our star, the sun. That’s a fraction of the mass in our galaxy, where billions of stars reside.

The newly detected object formed when the universe, estimated to be 14 billion years old, was not even a billion-year-old tyke. The object is 13.4 billion light-years from Earth, meaning that light from the object traveled for 13.4 billion years before reaching our telescopes.

The object is so faint it could not be detected using existing ground or space telescopes. Instead, scientists used a phenomenon called gravitational lensing to boost the power of those telescopes by more than 30 times.

When light passes by a massive object, the gravitational field of the object causes the light to bend. That phenomenon, first predicted by Einstein, turns a truly huge object, like a galactic cluster, into a natural lens that can bend and focus light coming from behind it.

The scientists used one of these “natural telescopes,” a dense cluster of galaxies called Abell 2218 that is 2 billion light-years from Earth, to detect the faint galaxy.

“Our strategy has been to use this cosmic magnification to find feeble objects,” said Richard Ellis, a cosmologist at Caltech and lead author of the study that will be published in the Astrophysical Journal.

The scientists pointed two telescopes, the Hubble Space Telescope and the ground-based Keck Telescope, through the gravitational lenses. The Hubble is famed for clear, sharp pictures free from the Earth’s distorting atmosphere. The 10-meter Keck is able to gather large amounts of light, even from faint objects.

Using the gravitational lens provided magnification power equivalent to a 57-meter telescope, scientists said. “The Keck is powerful,” said Ellis, “but without the cosmic lens, this object would never have been seen.”

Ellis suspects his team captured an image of a galactic building block when it was very young and before stars had even begun to form in it. The glow and particular wavelengths of light coming from the object are probably because of hot hydrogen gas being heated as new stars begin to form, he said.

“This particular object is being seen at a precious moment in its history. We think we’re witnessing the birth of a stellar system,” Ellis said.

“We’re looking for baby galaxies,” said Mike Santos, an astronomer and graduate student at Caltech who co-wrote the article with Ellis and two European astronomers, Jean-Paul Kneib and Konrad Kuijken. “These seeds, like people, grow.”

Many astronomers, including Ellis, remain somewhat cautious about the find. Because it is the first object of its kind to be seen and because some questions remain about how to precisely gauge the brightness of a feature through a gravitational lens, they’d like to confirm the find by studying it in more detail and with other telescopes or by finding more baby galaxies.

“There is considerable uncertainty to how much of a galaxy there is, but clearly this is a pretty small building block,” said Hyron Spinrad, a professor of astronomy at UC Berkeley and a pioneer in studies of galactic evolution. “We are in an infancy in this sort of study.”

Astronomers were most excited about the use of gravitational lensing to detect objects so faint. “It’s extremely promising,” said Arjun Dey, an astronomer at the National Optical Astronomy Observatory in Tucson who researches galactic evolution.

It will be at least a decade before astronomers begin using a new generation of high-power telescopes now in development; until then, gravitational lensing could prove very useful, he said.

Added Margon: “It’s so gorgeously economical to look in a direction where nature already put a telescope.”