Hubble detects ‘string of pearls’ celestial star clusters during galaxy collisions

When spectacular cosmic events such as galaxy collisions occur, they trigger a reaction to form new stars, and perhaps new planets that otherwise would not have formed. The gravitational pull that causes collisions between these galaxies creates tidal tails, the long, thin region of stars and interstellar gas.

The Hubble Space Telescope’s vision is so sharp that it can see clusters of newborn stars hanging along these tidal tails. They form when knots of gas gravitationally collapse to create about 1 million newborn stars per cluster.

Specifically, NASA’s Hubble Space Telescope focused on 12 interacting galaxies that have long tidal tails of gas, dust, and a plethora of tadpole-like stars. Hubble’s exquisite sharpness and sensitivity to ultraviolet light discovered 425 clusters of newborn stars along these tails, resembling strings of Christmas lights.

Each cluster contains up to 1 million newborn blue stars.

Clusters in tidal tails have been known for decades. When galaxies interact, tidal gravitational forces result in long streamers of gas and dust. Two popular examples are the Antennae and Mouse galaxies with their long, narrow finger-like projections.

In a study recently published in Monthly Notices of the Royal Astronomical Society Astronomers used the near-infrared capabilities of NASA’s Hubble Space Telescope to study tidal tail clusters and determine their ages and masses, as well as the properties of merging galaxies.

Michael Rodruck of Randolph-Macon College is the lead author of this study with co-authors including Arizona State University scientists Sanchayeeta Borthakur and Karen Knierman in the School of Earth and Space Exploration.

A team of astronomers used a combination of new observations and archival data to obtain the age and mass of tidal tail star clusters. They discovered that these clusters are very young: they are only 10 million years old. And they seem to form at the same rate along tails stretching thousands of light years.

“These observations tell us how stars form and what regulates these processes. This knowledge is essential for understanding how stars in our own galaxy formed,” said Associate Professor Sanchayeeta Borthakur, an observational astronomer specializing in astronomy. extragalactic at the ASU School of Earth. and space exploration.

The tails appear to take the spiral arm of a galaxy and extend it out into space. The outer part of the arm is pulled like taffy during the gravitational tug-of-war between two interacting galaxies.

Before the mergers, galaxies were rich in dusty clouds of molecular hydrogen that may have simply remained inert. But the clouds jostled and collided over the course of the encounters. This compressed the hydrogen to the point of precipitating a firestorm of star birth.

The fate of these star clusters is uncertain. They can remain gravitationally intact and evolve into globular star clusters, like those that orbit outside the plane of our galaxy, the Milky Way. Or they may disperse to form a halo of stars around their host galaxy, or be discarded to become wandering intergalactic stars.

“It is really exciting to present the culmination of more than two decades of work on star clusters in tidal tails using data from different Hubble epochs as well as those from other telescopes,” said the assistant professor Karen Knierman. “I started working on this project while I was a student at Penn State in 1999, and some of these same data and results are used here. We obtained additional data from a Hubble program for which I was (principal investigator) when I came to ASU in 2007.”

This string of pearls star formation may have been more common in the early universe, when galaxies collided with each other more frequently. These nearby galaxies observed by Hubble are an indicator of what happened a long time ago and therefore allow us to look into the distant past.

“It’s a surprise to see a lot of young objects in the tails. This tells us a lot about the efficiency of cluster formation,” Rodruck said. “With tidal tails, you will build new generations of stars that otherwise might not have existed.”