Galaxy appears little changed in 10 billion years
Andrew C. Fabian, Remco C. van den Bosch, MPIA/NASA/ESA
A galaxy just over 230 million light-years away in the nearby Perseus cluster looks as if it was snatched from the dawn of time and delivered to our galactic neighborhood, new observations reveal. The galaxy, NGC 1277, formed all its stars in a quick burst roughly 10 billion years ago — less than 4 billion years after the Big Bang. Then it appears to have abruptly switched off.
Observations published in the Jan. 10 Astrophysical Journal Letters show that stars throughout the galaxy are uniformly old and formed in a 100-million-year-long flash that created new suns at a rate of up to 1,000 per year. For comparison, our Milky Way gives birth to only a few suns each year.
“There is nothing in the local universe that is similar,” says coauthor Ignacio Trujillo, a research fellow at Spain’s Instituto de Astrofísica de Canarias. “We see an extremely different star formation history in the early universe compared to today.”
Most galaxies, including our own, grow by cannibalizing other galaxies. Every time one galaxy smashes into another, new gas pours in and sparks a wave of star formation. It’s a slow process that takes billions of years. Usually, hints of this violent past show up as streams of gas and stars. NGC 1277 shows none of this.
What researchers see in NGC 1277 is a galaxy that assembled most of its mass very quickly, including a gargantuan black hole at its center. The black hole, weighing in at 17 billion suns, is one of the most massive known and much heavier than astronomers would expect to find in a galaxy the size of NGC 1277. How it got there is a mystery (SN: 4/6/13, p. 12). Contrary to the standard picture of supermassive black holes slowly growing over many billions of years, the observations make clear that NGC 1277’s black hole formed fast and has been around for a very long time.
“It’s unusual to see an old stellar population formed in a burst in a disk galaxy,” says astronomer John Kormendy of the University of Texas at Austin. “Disks usually form very slowly; to have a disk this old … something prevented any kind of star formation since its beginning.”
Typically, the only way researchers can learn about galaxy birth is to look at very distant systems. Such galaxies are so distant that their light has taken nearly the age of the universe to reach Earth, so telescopes see them as they were in the first billion or so years after the Big Bang. At distances of billions of light-years, it’s hard to tease out much information; the galaxies are little more than smudges of light. However, computer simulations suggest that a very tiny fraction — just 0.1 percent — of nearby massive galaxies have gone their whole lives without running into a neighbor.
Though Trujillo thinks the galaxy survived by escaping collisions, Kormendy believes the hot gas that surrounds NGC 1277 has kept it well preserved.
“It’s not OK to make the assumption that it hasn’t done any interacting with its environment,” Kormendy says. Galaxies need cool gas to make stars. But the entire Perseus cluster is bathed in a gas at 10 million degrees Celsius, and Kormendy maintains that this gas is most likely stifling growth in the galaxy.
What’s more, while there are no signs of recent collisions, Kormendy thinks that NGC 1277 hasn’t escaped the influence of other galaxies: “It’s been whittled by interactions with neighbors and probably smaller than it was 5 billion years ago.” He adds that the galaxy may have lost up to half its mass, which may be the reason the central black hole appears so massive.
Regardless, Kormendy agrees that this is an ancient galaxy that formed quickly and then shut down, which is itself fascinating and surprising. “It’s not easy to understand anything about this galaxy,” he says. “It’s in an unusual volume of the universe where lots of mass collected very early into a collection of galaxies. [There is] something special about this environment.”
Editor's Note: This story was updated January 7, 2014, to correct how long ago the galaxy NGC 1277 formed its stars and to correct the weight of the black hole at the galaxy's center.
I. Trujillo et al. NGC 1277: a massive compact relic galaxy in the nearby universe. Astrophysical Journal Letters. Vol. 780, January 10, 2014, p. L20. doi:10.1088/2041-8205/780/2/L20.
A. Grant. New home for runaway black hole. Science News. Vol. 183, April 6, 2013, p. 12.