'Dead' galaxies aren't so dead after all, U-M researchers find

May 31, 2011

ANN ARBOR, Mich.---University of Michigan astronomers examined old galaxies and were surprised to discover that they are still making new stars. The results provide insights into how galaxies evolve with time.

U-M research fellow Alyson Ford and astronomy professor Joel Bregman presented their findings May 31 at a meeting of the Canadian Astronomical Society in London, Ontario.

Using the Wide Field Camera 3 on the Hubble Space Telescope, they saw individual young stars and star clusters in four galaxies that are about 40 million light years away. One light year is about 5.9 trillion miles.

"Scientists thought these were dead galaxies that had finished making stars a long time ago," Ford said. "But we've shown that they are still alive and are forming stars at a fairly low level."

Galaxies generally come in two types: spiral galaxies, like our own Milky Way, and elliptical galaxies. The stars in spiral galaxies lie in a disk that also contains cold, dense gas, from which new stars are regularly formed at a rate of about one sun per year.

Stars in elliptical galaxies, on the other hand, are nearly all billions of years old. These galaxies contain stars that orbit every which way, like bees around a beehive. Ellipticals have little, if any, cold gas, and no star formation was known.

"Astronomers previously studied star formation by looking at all of the light from an elliptical galaxy at once, because we usually can't see individual stars," Ford said. "Our trick is to make sensitive ultraviolet images with the Hubble Space Telescope, which allows us to see individual stars."

The technique enabled the astronomers to observe star formation, even if it is as little as one sun every 100,000 years.

Ford and Bregman are working to understand the stellar birth rate and likelihood of stars forming in groups within ellipticals. In the Milky Way, stars usually form in associations containing from tens to 100,000 stars. In elliptical galaxies, conditions are different because there is no disk of cold material to form stars.

"We were confused by some of the colors of objects in our images until we realized that they must be star clusters, so most of the star formation happens in associations," Ford said.

The team's breakthrough came when they observed Messier 105, a normal elliptical galaxy that is 34 million light years away, in the constellation Leo. Though there had been no previous indication of star formation in Messier 105, Ford and Bregman saw a few bright, very blue stars, resembling a single star 10 to 20 times the mass of the sun.

They also saw objects that aren't blue enough to be single stars, but instead are clusters of many stars. When accounting for these clusters, stars are forming in Messier 105 at an average rate of one sun every 10,000 years, Ford and Bregman concluded. "This is not just a burst of star formation but a continuous process," Ford said.

These findings raise new mysteries, such as the origin of the gas that forms the stars.

"We're at the beginning of a new line of research, which is very exciting, but at times confusing," Bregman said. "We hope to follow up this discovery with new observations that will really give us insight into the process of star formation in these 'dead' galaxies."
-end-


University of Michigan

Related Hubble Space Telescope Articles from Brightsurf:

Spitzer space telescope legacy chronicled in Nature Astronomy
A national team of scientists Thursday published in the journal Nature Astronomy two papers that provide an inventory of the major discoveries made possible thanks to Spitzer and offer guidance on where the next generation of explorers should point the James Webb Space Telescope (JWST) when it launches in October 2021.

Unveiling rogue planets with NASA's Roman Space Telescope
New simulations show that NASA's Nancy Grace Roman Space Telescope will be able to reveal myriad rogue planets - freely floating bodies that drift through our galaxy untethered to a star.

Hubble makes the first observation of a total lunar eclipse by a space telescope
Taking advantage of a total lunar eclipse, astronomers using the NASA/ESA Hubble Space Telescope have detected ozone in Earth's atmosphere.

Stunning space butterfly captured by ESO telescope
Resembling a butterfly with its symmetrical structure, beautiful colours, and intricate patterns, this striking bubble of gas -- known as NGC 2899 -- appears to float and flutter across the sky in this new picture from ESO's Very Large Telescope (VLT).

Hubble marks 30 years in space with tapestry of blazing starbirth
NASA is celebrating the Hubble Space Telescope's 30 years of unlocking the beauty and mystery of space by unveiling a stunning new portrait of a firestorm of starbirth in a neighboring galaxy.

CHEOPS space telescope ready for scientific operation
CHEOPS has reached its next milestone: Following extensive tests in Earth's orbit, some of which the mission team was forced to carry out from home due to the coronavirus crisis, the space telescope has been declared ready for science.

Scientists build a 'Hubble Space Telescope' to study multiple genome sequences
Scientists can now simultaneously compare 1.4 million genetic sequences, helping classify how species are related to each other at far larger scales than previously possible.

Kepler Space Telescope's first exoplanet candidate confirmed
An international team of astronomers announced the confirmation of the first exoplanet candidate identified by NASA's Kepler Mission.

Space telescope detects water in a number of asteroids
Using the infrared satellite AKARI, a Japanese research team has detected the existence of water in the form of hydrated minerals in a number of asteroids for the first time.

The Hubble Space Telescope discovers the most distant star ever observed
An international team, including researchers from the Instituto de AstrofĂ­sica de Canarias (IAC) and the University of La Laguna (ULL), participated in the discovery of a star at a distance of nine billion lightyears from Earth.

Read More: Hubble Space Telescope News and Hubble Space Telescope Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.