Can you see the dwarf galaxies in the above image, shot by the Hubble Space Telescope? Yeah, me neither. But they’re there, and some of them are working exceptionally hard to make new stars. I’ve included a cheat sheet below so you’ll know which of the galaxies in the image are some of the ones scientists looked at during a recent survey of star formation in the early universe.
Many of the stars we see in the universe today were formed between two and six billion years after the Big Bang. But until now, astronomers didn’t really know how many of those stars were born in dwarf galaxies — the small, low-mass clusters of several billion stars that are too big to be normal star clusters and too small to be regular galaxies. Today, we tend to see dwarf galaxies clinging to or clumped around larger galaxies, rather than existing as blazing collections of stars in their own right.
But scientists had suspected that dwarfs in the early universe — an age pre-dating the evolution and growth of many super-huge galaxies — contributed something substantial to the overall amount of stars. The trouble is, they really had no way of measuring how quickly these small galaxies produced stars. Most images weren’t sharp enough to reveal the faint, faraway galaxies teams needed to observe.
Now, though, images from the Hubble Space Telescope are helping scientists chip away at that answer. Using data from the Hubble Wide Field Camera 3 — which looks at the sky in infrared wavelengths — scientists were able to study a sample of dwarf galaxies in the early universe. Within this sample are starburst galaxies, or galaxies with abnormally high rates of star formation. And some of them are working overtime to churn out new stars. In fact, the rate at which stars are turning on in those starbursting dwarfs is most unexpected, the team reports June 19 in The Astrophysical Journal.
“These galaxies are forming stars so quickly that they could actually double their entire mass of stars in only 150 million years — this sort of gain in stellar mass would take most normal galaxies 1-3 billion years,” says study co-author Jean-Paul Kneib of the Ecole Polytechnique Federale de Lausanne, in Switzerland.
The team doesn’t yet know why these small galaxies are such overachievers. In general, bursts of star formation are thought to follow somewhat chaotic events like galactic mergers or the punch of a supernova’s shockwave. But by continuing to study these dwarf galaxies, scientists hope to learn more about galactic evolution and star formation during the universe’s childhood.