Where Do Babies Come From?*
*Baby Dwarf Galaxies, That Is
In the 13.7-billion-year-long history of the universe, we know that galaxies had to come from somewhere, right? It’s obvious that they were born, and we’re sitting inside one. And, since we can look out across great distances and see further back in time), you’d think we would be able to find galaxy “babies”. But, explaining the processes involved in galaxy building and observing them in action has been difficult. Part of the problem is that the galaxy formation section of our universe (if you want to think of it that way) is pretty far distant from us. That makes it tough to “see” unless you can look at galaxy birthplaces in different wavelengths of light.
The Galaxy Evolution Explorer (GALEX, a project run by NASA) looked out at the galaxy birthing fields in the universe with ultraviolet eyes and turned up some pretty interesting action. Specifically, scientists using GALEX identified dwarf galaxies being born in clouds of pristine gas that could well have been left over from the creation of the universe itself.
Forming dwarf galaxies shine in ultraviolet light (objects in circles) as seen by the GALEX mission. The circled clumps are the dwarf galaxies found by the mission. Visible-light data (white) comes from the Digitized Sky Survey (STScI). The blue overlay comes from radio data provided by Arecibo Observatory. (Click to embiggen.)
They found unexpected new galaxies forming inside the Leo Ring, a huge cloud of hydrogen and helium that seems to hover around two huge galaxies in the constellation Leo. The whole complex lies around 35 million light-years away from us.
The cloud, which lies about 35 million light-years away from us, was first identified about 25 years ago in radio astronomy data. It’s not something you can see in visible light through an optical telescope. Astronomers have tried exploring this ring, and all they found was gas. No stars of any kind could be seen at optical or radio wavelengths. But, the GALEX satellite, with its ultraviolet light sensitivity found evidence of recent massive star formation in this region.
So, what’s the “smoking gun” signature of star formation in this ring? The ultraviolet signature of young stars is clearly seen coming from several clumps of gas within the Leo Ring. Astronomer David Thilker of Johns Hopkins University thinks they’re dwarf galaxies. “We speculate that these young stellar complexes are dwarf galaxies, although, as previously shown by radio astronomers, the gaseous clumps forming these galaxies lack dark matter,” he said. “Almost all other galaxies we know are dominated by dark matter, which acted as a seed for the collection of their luminous components — stars, gas and dust. What we see occurring in the Leo Ring is a new mode for the formation of dwarf galaxies in material remaining from the much earlier assembly of this galaxy group.”
Because they lack dark matter, these new galaxies astronomers are seeing in the Leo Ring resemble tidal dwarf galaxies (the kind that condense out of gas recycled from other galaxies), but there’s an important difference. The gaseous material making up tidal dwarfs is rich with metals and elements that could only have been created inside stars. The Leo Ring dwarfs are made of much more pristine material that doesn’t have ANY metals in it. Which means that no stars formed to “pollute” the gas making up the Leo Ring dwarfs. Which gives astronomers a rare and new chance to study star formation in gases that are pristine leftovers from the creation of the universe. There may have been a lot of these “pure” gas clouds early in universal history. As astronomers look farther out in space and further back in time with instruments like GALEX, they may find more of these baby galaxies being born.
You can get more information and images here about these baby galaxies and the GALEX mission.
