Galaxies far, far away

The most distant galaxies ever seen appear in this image taken last year by the Hubble Space Telescope. The faintest objects (circled above and enlarged in the grid below) represent primordial galaxies, the digital imprints of starlight that left those galaxies just 600 million to 700 million years after the Big Bang and traveled across the universe for 13 billion years to reach Hubble's detectors. (Photo by Hubble Wide Field Camera 3)

Like everyone else, UCSC astronomers are forced to live in the present. But with the help of the Hubble Space Telescope, they are peering further and further into the past.

"We're asking one of the grandest questions of existence: where do things come from?" says David Koo, professor of astronomy and astrophysics.

The groundbreaking work of UCSC astronomers has already revealed the most distant galaxies ever seen. Their latest project will gather enough new information about the distant universe to occupy scientists for years, bridging the gap between current instruments and more powerful telescopes planned for the future.

Now two decades old, Hubble is in the last stage of its life, but a new instrument, the Wide Field Camera 3 (WFC3), has given it unprecedented abilities--and UCSC astronomers are exploiting it to discover new galaxies, exploring the universe as never before.

"Hubble is now more powerful than it has ever been in the past," says Koo. He's on a team led by professor of astronomy and astrophysics Sandra Faber that will use a record amount of observing time on Hubble, opening the telescope's eyes to the universe for two months.

'Rich' science

Astronauts installed the WFC3 during Hubble's last servicing mission in May 2009. The camera takes pictures in visible wavelengths as well as ultraviolet and the near-infrared, which have wavelengths that are shorter and longer, respectively, than what our eyes can see.

"This camera is incredibly powerful--a red-sensitive camera that's taking pictures in ways that we couldn't before," Faber says. "The science we'll study is extremely rich."

Garth Illingworth

Astronomer Garth Illingworth leads the Hubble Ultra Deep Field 2009 project, which found the most distant galaxies ever seen. (Photo by Jim MacKenzie)

Professor of astronomy and astrophysics Garth Illingworth is already demonstrating the power of this new camera, leading a team that has discovered the most distant galaxies yet. Because light from these distant galaxies takes billions of years to reach Hubble's mirrors, the telescope acts as a time machine, providing astronomers with pictures of the cosmos as it was billions of years ago. The deeper Hubble looks into space, the farther it gazes into the universe's 13.7 billion-year history.

"When we first saw the data, we were just astonished at the quality," Illingworth remarks. "We were doing things that would've been impossible with the old cameras on Hubble." The new camera is 40 times better at finding these early galaxies, he says.

Illingworth and his team, which includes UCSC astronomer Rychard Bouwens and researcher Daniel Magee, pointed the telescope at the Hubble Ultra Deep Field (HUDF), a small patch of sky about one-tenth the size of the moon, that was first studied in 2004 with the Advanced Camera for Surveys, an instrument for which Illingworth was a deputy principal investigator.

That initial data set contains the most distant pictures ever taken in visible wavelengths--reaching back to 900 million years after the Big Bang--and by combining it with the deepest-ever infrared images of the universe from Illingworth's WFC3 survey of HUDF, the researchers discovered galaxies from just 600 million to 800 million years after the Big Bang.

"This is really impressive," Illingworth says. "The analogy I've used is that if the universe is an 80-year-old person, we're looking back to when it was a toddler--just three or four years old."

The team has also found three tiny blobs of light that appear to be galaxies dating back to when the universe was merely 500 million years old.

Galactic seeds

The astronomers took data in August 2009 and February 2010, and will finish their run this fall for a total of 13 days of observations. So far, they've found 105 of these early galaxies, resulting in a flurry of research papers over the last few months, written by the team and other astronomers. At about one-twentieth of the size of the Milky Way and at 1 percent of the mass, these faint smudges were the seeds that merged and grew into the majestic galaxies we see today.

Galaxy imagery
Surprisingly, these early galaxies were very blue, Illingworth says, suggesting a lack of dust and perhaps of the heavier elements that were later forged in stars like our Sun. The astronomers also discovered that the 600- to 800-million-year old galaxies were already forming stars 300 million years prior, much closer to the time when the first stars in the universe were born.

"That's a remarkable result," he says.

These first galaxies filled the universe during a period called reionization, when all the hydrogen gas in the cosmos somehow became ionized, its electrons stripped away by some source of ultraviolet light. The identity of this source has been a long-standing mystery, and studying these galaxies may provide much-needed clues--is there enough bright ultraviolet light that escapes from these galaxies? Are there enough galaxies to begin with?

Hubble's last hurrah

While Illingworth's HUDF survey focused on three small areas in the sky with the deepest-ever near-infrared images, Faber's upcoming project covers a spectacular 70-times-larger area less deeply over five well-studied regions.

"They're perfectly complementary, deep and wide," Illingworth says. "They go hand in hand."

Sandra Faber

Astronomer Sandra Faber leads the Cosmology Survey Multi-Cycle Treasury Program, which will survey more than 250,000 distant galaxies. (Photo by Jim MacKenzie)

Faber's survey will also stretch back to 600 million years after the Big Bang, snapping pictures of galactic nurseries and compiling a census of these infants to see how they grow and what sorts of environments surround them.

"This presses the limit of this camera to the very edge," Faber says. "With our survey, we're going to have a much larger area and we're going to be able to count these [young galaxies] for the first time very accurately."

Also led by co-principal investigator Henry Ferguson of the Space Telescope Science Institute in Baltimore, the newest survey will start at the end of the year and take three years to complete. With Hubble near retirement, this project could be its last hurrah, complementing ground-based telescopes and other space telescopes, such as the Spitzer Space Telescope and the Chandra X-ray Observatory.

"We're adding that final, wonderful data set to make a lasting legacy of those five key regions for studying distant galaxies," Koo says.

Faber's team is interested in the time when the universe was just a few billion years old, when it was abuzz with galactic activity. Star births were booming, galaxies were crashing into each other at a high clip, and lots of exotic behemoths called supermassive black holes--which are millions or billions of times as massive as the Sun--were gobbling up gas and dust at galactic centers, generating enormous amounts of heat and energy as quasars, the brightest objects in the cosmos. To understand galaxies today requires understanding galaxies during this period, which Faber calls the high-water mark of galaxy formation--akin to the growth spurts of adolescence.

Previously, Hubble wasn't able to see the redder, older stars, and so its images of galaxies were incomplete, appearing ragged and irregular. But in their survey, Faber explains, they'll be able to detect this "scaffolding of older stars," as she calls it, revealing the detailed structure of galaxies. The new camera will also be able to discern these stellar seniors near the center of galaxies, where supermassive black holes lurk. The black hole tugs at the swarm of stars around it, altering trajectories and velocities. Snapshots that include the older stars would help reveal how a humongous black hole influences the shape and size of its galaxy.

Expanding universe

The team also anticipates discovering about a dozen of the most distant Type 1a supernovae, stellar explosions that all appear to detonate with the same amount of energy. The apparent brightness of these supernovae allows astronomers to gauge how far they are, providing a ruler to measure the size of the universe and, most importantly, how fast it's expanding.

In fact, it was this type of supernova that led astronomers more than a decade ago to discover that the expansion is accelerating, implying the existence of a mysterious force called dark energy.

But, Faber says, we can't be sure Type 1a supernovae haven't changed over time, resulting in unreliable measurements of dark energy. For one thing, stars in the early universe boasted fewer heavy elements, possibly leading to explosions unlike

those of present-day supernovae.

The expanding universe adds another layer of uncertainty to the calculations, as astronomers' interpretation of supernovae depends on the shape of the universe, which is itself strongly influenced by dark energy. But early on, when the universe was about 5 billion years old, matter was more densely packed together, and so gravity was more important than dark energy. As the cosmos expanded, the space between galaxies grew and the effect of gravity waned while dark energy remained constant and gained influence. So by studying Type 1a supernovae before dark energy held sway, astronomers could compare them to today's supernovae and better calibrate the cosmic measuring sticks.

In the next decade, several bigger telescopes will come online. The James Webb Space Telescope, an infrared instrument, is slated to launch in 2014. Other ground-based scopes include the Thirty Meter Telescope in Hawaii--for which the University of California is a partner institution--the European Extremely Large Telescope, and the Atacama Large Millimeter Array in Chile.

But once Hubble retires, Faber's survey will be the last big stockpile of data for at least several years. The database will then help astronomers identify targets to focus on with these larger telescopes, serving as a bridge to the future, Koo says.

"It's not the culmination or the end," he says, "but an extremely important next advance."

And UCSC astronomers are leading these two remarkable Hubble projects, whose legacy will stretch into the next decade.

Marcus Woo is a 2007 graduate of UCSC's science writing program. He lives in Pasadena.