Astronomers discover ‘mirror image’ of Milky Way from billions of years ago

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

It is nicknamed “The Sparkler”. That’s because it has about two dozen bright globular clusters orbiting around it. There are also some dwarf galaxies there, being swallowed up by the galaxy.

The JWST view shows Sparkler as it was when the Universe was just four billion years old, or about a third of the Universe’s current age. This implies that this galaxy, like the Milky Way, began to form very early in cosmic history.

If Sparkler follows the same growth path that the Milky Way did through galaxy mergers and acquisitions, it should grow in the same way as the Milky Way. In about nine billion years, it could look a lot like our twin.

A distant and early proxy for our Milky Way

The Sparkler is in the direction of the constellation of Volans (in the sky of the southern hemisphere). It is quite far away, with a redshift of z = 1.38. That’s about 9 billion light years and puts it at a time a few billion years after the Big Bang. Like the Milky Way, Sparkler did not emerge from the fully formed cosmos.

Both galaxies began as “superdensities” of matter (like clouds of neutral hydrogen) in the early Universe. Think of them as galactic “seeds” attracted by the gravitational pull they exert on each other. Globular clusters were born in some of these clusters, probably just before the birth of the galaxy. This is why the stars in some globulars are older than their galaxies.

Then came an era of “mergers and acquisitions”, as the young Milky Way (and presumably Sparkler as well) began to cannibalize nearby dwarf galaxies. This is a huge evolutionary step. It is possible that at least half of the mass of our own galaxy came from these mergers. Over time, all the material merged into the spiral disk where the Sun and most other stars exist today.

Sparkler’s future compared to the Milky Way

Will Sparkler follow the same evolutionary path as the Milky Way? From the JWST data, it seems so. Although it is currently only a small fraction of the mass of the Milky Wayabout 3 percentthis will change as it engulfs other smaller galaxies. Eventually, it will match the mass of the Milky Way in the current Universe.

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

“We seem to be witnessing first-hand the assembly of this galaxy as it increases in the form of a dwarf galaxy and several globular clusters,” said Professor Duncan Forbes of Swinburne University in Australia.

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

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

Forbes and Romanowsky used the JWST data to explore the ages and metallicities of various “bright” (compact sources) in and around the Sparkler galaxy. The aim was to study metallicity in a series of compact star clusters around Sparkler. Scientists wanted to see if they resembled younger versions of globulars in the Milky Way.

Clues to Sparkler’s early history in its globular clusters

Sparkler’s JWST observations could also answer a number of questions about globular clusters and their formation, according to Romanowsky. “The origin of globular clusters has been a longstanding mystery,” he said. “We are thrilled that JWST can look back in time to see them in their youth.”

It turns out that Sparker’s clusters bear striking similarities to some of the Milky Way’s globulars. Several appear to have formed very early on, and the stars are quite rich in metals. This seems to indicate a very rapid process of chemical enrichment in the early Universe.

Some clusters had stars that were slightly older and metal-poor than other clusters. They likely belong to a low-mass satellite galaxy that is being ingested by Sparkler. The scene is very reminiscent of the history of Milky Way mergers throughout its lifetime.

More data needed

To gain a better understanding of the evolutionary state of Sparkler and its clusters, the two scientists say more observations of similar-type clusters around other distant galaxies in the universe are needed. This would help determine whether Sparkler is typical of the merging style of galactic evolution (similar to the Milky Way).

Otherwise, the details of early galaxy evolution, chemical enrichment, mass growth, and star cluster formation may need some revision.

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

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