They might be small, but that doesn't stop dwarf galaxies from cooking up a lot of stars. According to new Hubble observations, dwarf galaxies are responsible for forming a large proportion of the universe’s stars.
The early universe, between 2 and 6 billion years after the Big Bang, was an important time when most stars were formed. For the last decade, astronomers have been looking for a link between a galaxy’s mass and its star-forming activity, but previous studies of stellar births during this epoch were limited to mid- or high-mass galaxies -- leaving low-mass dwarf galaxies out of this formative era of prolific star formation.
"We already suspected these kinds of galaxies would contribute to the early wave of star formation, but this is the first time we've been able to measure the effect they actually had," says Hakim Atek of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. “They appear to have had a surprisingly huge role to play."
Using the infrared capabilities of Hubble’s Wide Field Camera 3 (WF3), Atek and colleagues were able to examine a sample of “starburst galaxies” in the young universe. Starburst galaxies are ones that churn out stars at a crazy fast rate -- far above normal expectations. With these observations, the team was able to calculate how much dwarf galaxies contributed to our universe’s star population.
"These galaxies are forming stars so quickly they could actually double their entire mass of stars in only 150 million years -- an incredibly short astronomical timescale," study coauthor Jean-Paul Kneib of EPFL says in a news release. Massive growth like that would take normal galaxies 1 to 3 billion years.
The image above (and annotated below) shows a region of space containing thousands of galaxies, including a sample of distant and faint dwarf galaxies residing in the early universe. Some of them can be seen forming stars at a furiously fast rate.
Additionally, because it’s unusual to find a galaxy in a state of starburst, the observations suggest that starburst galaxies may be the result of an unusual incident in the past, such as a violent galaxy merger or a supernova explosion.
The findings were published in the Astrophysical Journal this week.
Image: NASA, ESA, the GOODS Team, and M. Giavalisco (University of Massachusetts, Amherst)