Astronomers find ‘mirror image’ of Milky Way billions of years ago: ScienceAlert

Have you ever wondered what our Milky Way looked like in its early history? Astronomers using the Webb Telescope (JWST) have found another galaxy that is almost a mirror image of our galaxy as an infant.

It is nicknamed “The Sparkler”. That’s because it’s orbited by about two dozen glittering globular star clusters. There are also a few dwarf galaxies that are being swallowed up by the galaxy.

The JWST view shows the sparkler as it appeared when the universe was only four billion years old, or about one-third the age of the universe today. This means that this galaxy, like the Milky Way, began forming very early in cosmic history.

If the sparkler follows the same growth path as the Milky Way through mergers and acquisitions of galaxies, then it should grow as the Milky Way does. In about nine billion years, it could look very similar to our twin.

A distant, early proxy for our Milky Way

The sparkler lies in the direction of the constellation of Volans (in the sky of the southern hemisphere). It’s quite far away, at z=1.38 redshift. That is about 9 billion light years and thus a few billion years after the Big Bang. Like the Milky Way, the sparkler did not fully ascend out of the cosmos.

Both galaxies began as “overdensities” of matter (like clouds of neutral hydrogen) in the early Universe. Think of them as “seeds” of galaxies drawn in by their mutual gravitational pull. The globular clusters were born in some of these clumps, likely just before the galaxy was born. Therefore, the stars in some globular stars are older than their galaxies.

Next came an era of “mergers and acquisitions,” as the young Milky Way (and presumably the Sparkler, too) began cannibalizing nearby dwarf galaxies. This is a big evolutionary step. It’s possible that at least half the mass of our own galaxy came from these mergers. Over time, all of the material coalesced into the spiral disk on which the Sun and most other stars exist today.

The future of the sparkler compared to the Milky Way

Will the sparkler follow the same evolutionary path as the Milky Way? JWST data suggests that will be the case. Although currently it is only a small fraction of the mass of the Milky Way – about 3 percent – that will change as it engulfs other, smaller galaxies. Eventually it will reach the mass of the Milky Way in today’s Universe.

This is pretty exciting because it gives astronomers a chance to understand what happened as our own galaxy evolved.

“We appear to be witnessing firsthand the assembly of this galaxy as it builds mass – in the form of a dwarf galaxy and several globular star clusters,” said Professor Duncan Forbes of Swinburne University in Australia.

He studied the galaxy and its clusters with Professor Aaron Romanowsky of San Jose State University in California.

“We are excited about this unique opportunity to study both globular cluster formation and a young Milky Way at a time when the Universe was only 1/3 its current age,” he said.

Forbes and Romanowsky used the JWST data to study the age and metallicity of several “sparks” (compact sources) in and around the Sparkler Galaxy. The goal was to probe the metallicity over a series of compact star clusters surrounding the sparklers. The scientists wanted to see if they resembled younger versions of the Milky Way’s globular stars.

Clues to the early history of the sparkler in their globular clusters

The JWST observations of the sparklers could also answer various questions about globular clusters and their formation, according to Romanowsky. “The origin of globular clusters is a long-standing mystery,” he said. “We are thrilled that JWST can look back in time to see her in her youth.”

The Sparker clusters turn out to bear striking resemblances to some of the Milky Way’s globular stars. Several appeared to have formed very early, and the stars are quite metal-rich. This seems to indicate a very rapid process of chemical enrichment in the early universe.

A few clusters had stars that were slightly older and less metal-rich than in other clusters. They likely belong to a low-mass satellite galaxy included in the Sparklers. The scenery is strongly reminiscent of the Milky Way’s merging history throughout its lifetime.

More data required

According to the two scientists, further observations of similar clusters around other distant galaxies in the Universe are needed to better understand the evolutionary state of the sparklers and their clusters. This would help determine if the sparkler is typical of the merger style of galaxy evolution (similar to the Milky Way).

If not, the details of early galaxy evolution, chemical enrichment, mass growth, and star cluster formation may need to be revised.

This article was originally published by Universe Today. Read the original article.

Leave a Reply

Your email address will not be published. Required fields are marked *