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A Long Time Ago in a Galaxy Far, Far Away…There Were These Little Blue Dots

Debra Elmegreen, Vassar’s Maria Mitchell Professor of Astronomy, has spent much of her career studying the structure and origins of galaxies throughout the universe. She and her husband kicked off 2018 by announcing the discovery of some low-mass galaxies unlike anything anyone had ever seen.

Using data and photographs from the Hubble Space Telescope, Prof. Elmegreen and her husband, IBM astronomer Bruce Elmegreen, detected what appeared to be tight clusters of rapidly forming stars in the early stages of the formation of the universe. “We kept finding these little blue dots,” Prof. Elmegreen says. Since these dwarf galaxies were smaller than some that had been dubbed “blueberries” by the astronomers who found them, the Elmegreens decided to call their discovery “Little Blue Dots.”

Elmegreen points to the blue dots in an enlargement of a Frontier Field image from the Hubble Space Telescope.

“Ordinarily, I don’t like the cute names that astronomers sometimes call their discoveries,” Prof. Elmegreen says, “but in this case, that’s exactly what they are. We found 55 of them, and they are a kind of galaxy never seen before.”

In a paper on their discovery published Jan. 2, the Elmegreens surmise that these Little Blue Dots wind down their rapid star formation “after a few tens of millions of years” and eventually become the precursors to globular clusters, common aggregations of stars found in most large galaxies.

The discovery is significant because it sheds further light on how galaxies formed and evolved when the universe was one-fifth to one half of its current age of about 14 billion years. Galaxies like these must eventually have merged with larger galaxies like the Milky Way to become part of galaxy halos.

The Hubble Space Telescope Frontier Fields project captured images of six massive galaxy clusters. Pictured here is the Abell 370 cluster, some 5 billion light-years away. While one of the Hubble’s cameras focused on each of the six clusters, a second camera captured the adjacent regions called “parallel fields.” The Elmegreens’ study of the parallel fields revealed the Little Blue Dots (not visible in this image of the Abell 370).

Prof. Elmegreen says she and her husband first spotted the Little Blue Dots last September. They were using the Hubble Space Telescope to observe images of fields parallel to six large galaxy clusters in what is known as the Frontier Fields project. It was in this deep space that they found the Little Blue Dots. She said she was glad she and her husband had made such a significant discovery together. “We’ve always had such fun working together,” she says.

While she is part of several teams of astronomers who use the Hubble Space Telescope and many of the major ground-based telescopes around the world, Prof. Elmegreen says her position as a professor at a small liberal arts college also affords her plenty of autonomy. “Because I’m at a small institution, I have the advantage of not just being part of one large team that has its next step of research all mapped out,” she says. “It’s nice to be part of different collaborations, but I also have the freedom to work on whatever research appeals to me.”

Whatever she chooses to explore next, Prof. Elmegreen says she’s certain there are many new discoveries ahead for her and many other astronomers. “With the Hubble going up in 1990 and the much larger James Webb Space Telescope due to launch in a year or so, it’s an unbelievable time to be an astronomer,” she says. “As Bruce and I look back on the progress of the last 40 years we’ve been in the business, we’re certain the next 40 years will be amazing.”