Pisces A (left) and Pisces B (right); two galaxies that have been pulled into a crowded region of space and begun star formation anew. Credit: NASA, ESA, and E. Tollerud (STScI)
The Hubble Space Telescope has captured two previously lone dwarf galaxies wandering into a crowded galactic region, offering a snapshot of the early Universe.
Galaxies Pisces A and B have spent most of their existence in the Local Void, which is a 150 million lightyear-wide empty area of space near the Local Group, but have now found a new home in a crowded, gas-rich environment.
While their former isolation has given them a relatively uneventful existence so far, interactions with their newfound galactic brethren have instigated a new era of energetic star formation.
The galaxies were pulled towards the crowded area from the Local Void by the gravitational pull of massive objects in the Local Group.
The presence of cosmic gas and dust in their new home is providing the materials they need to make new stars.
As well as giving an insight into how stellar formation is triggered, these dwarf galaxies could help reveal how galaxies existed in the early Universe.
Dwarf galaxies are thought to be the small building blocks from which larger galaxies eventually formed in the early Universe as they interacted with other galaxies of the same size.
But as Pisces A and B existed in the Local Void for so long, they avoided the busy period as the Universe began to develop.
Evidence for the galaxies’ previous home in the Local Void comes from their high hydrogen content, relative to similarly sized galaxies.
Hydrogen is a key fuel in stellar formation and early galaxies contained it in abundance, before eventually using it up as they grew and generated more stars.
As Pisces A and B have high concentrations of hydrogen, it follows that they have not used the star-forming gas up at the same rate as they have spent most of their lives isolated.
Astronomers found the galaxies as part of a survey measuring the hydrogen content in the Milky Way.
The dwarf galaxies are so small they would otherwise have been difficult to find.
Each galaxy contains about 20 to 30 bright blue stars, indicating that they are less than 100 million years old.
Pisces A is about 19 million lightyears from Earth, while Pisces B is about 30 million lightyears away.
“These Hubble images may be snapshots of what present-day dwarf galaxies may have been like at earlier epochs,” says lead researcher Erik Tollerud of the Space Telescope Science Institute in Baltimore, Maryland.
“Studying these and other similar galaxies can provide further clues to dwarf galaxy formation and evolution.”