New Delhi:

Earliest “building blocks” of our Milky Way galaxy have been identified from 12-13 billion years ago, which is very close in time to when the universe’s first galaxies started to form, according to a new research.

Naming these groups of stars ‘Shakti’ and ‘Shiva’, astronomers said the findings are the equivalent of “finding traces of an initial settlement that grew into a large present-day city”.

Milky Way is said to have formed by the merging of smaller galaxies, making way for “fairly large building blocks”, according to the researchers.

When galaxies collide and their stellar populations mingle, most of the stars retain very basic properties, directly linked to the speed and direction of their origin galaxy, they explained.

In this study published in The Astrophysical Journal, the research team from Max Planck Institute for Astronomy, Germany, analysed stellar datasets and found that stars from the merging galaxies were crowded around two specific signatures of energy and angular momentum, or the rate at which a spinning object’s rotating speed changes. Two different star groups were thus formed — ‘Shakti’ and ‘Shiva’.

The study’s co-author Khyati Malhan named these two structures Shakti and Shiva, the latter one of the principal deities of Hinduism and the former a female cosmic force often portrayed as Shiva’s consort.

The researchers found that the “like-minded” stars forming Shakti and Shiva, and coming from two different galaxies, had a higher angular momentum compared to the stars at the heart of the Milky Way.

The higher angular momentum observed was consistent with the stellar groups that had belonged to separate galaxies merging with the Milky Way, the team said.

Also, all these stars were low in metal content, signalling that they were formed a long time ago. Stars formed recently contain more of heavier metallic elements, they explained.

Therefore, their energy and angular momentum, along with low metallic content, comparable with that of the stars at the heart of Milky Way, makes ‘Shakti’ and ‘Shiva’ good candidates for some of the earliest ancestors of our Milky Way, the researchers said.

“Shakti and Shiva represent two of those early, massive progenitors that coalesced at high redshift – perhaps 12 gigayears ago – perhaps the last event from the protogalaxy before disk formation commenced,” they wrote in their study. A gigayear has a billion years.

Shakti and Shiva might be the first two additions to the heart of the Milky Way, initiating its growth towards a large galaxy, said study co-author Hans-Walter Rix from Max Planck Institute for Astronomy.

For their analysis, the researchers used the data provided by the European Space Agency’s Gaia satellite and combined it with the stellar datasets from the US Sloan Digital Sky Survey, having detailed information about the stars’ chemical composition.

Launched in 2013, Gaia’s dataset now includes positions, changes in the positions and distances for almost 1.5 billion stars within our galaxy, providing an ideal dataset for this kind of “big data galactic archeology”, the team said.
 

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

This handout photograph released by the CEA on September 7, 2023, shows a 3D representation of the galaxy “Bubble”, coloured in brown. The image shows the position of the Milky Way, with a small white dot located outside the bubble on the right, in a white cloud. The blue wisps represent the “cosmic web”, the filaments of galaxies that make up other large structures in the Universe, such as Laniakea.
| Photo Credit: AFP

Astronomers have discovered the first “bubble of galaxies,” an almost unimaginably huge cosmic structure thought to be a fossilised remnant from just after the Big Bang sitting in our galactic backyard.

The bubble spans a billion light years, making it 10,000 times wider than the Milky Way galaxy.

Yet this giant bubble, which cannot be seen by the naked eye, is a relatively close 820 million light years away from our home galaxy, in what astronomers call the nearby universe.

The bubble can be thought of as “a spherical shell with a heart,” Daniel Pomarede, an astrophysicist at France’s Atomic Energy Commission, told AFP.

Inside that heart is the Bootes supercluster of galaxies, which is surrounded by a vast void sometimes called “the Great Nothing”.

The shell contains several other galaxy superclusters already known to science, including the massive structure known as the Sloan Great Wall.

Pomarede said the discovery of the bubble, which is described in research he co-authored that was published in The Astrophysical Journal this week, was “part of a very long scientific process”.

It confirms a phenomenon first described in 1970 by US cosmologist — and future physics Nobel winner — Jim Peebles.

He theorised that in the primordial universe — then a stew of hot plasma — the churning of gravity and radiation created sound waves called baryon acoustic oscillations (BAOs).

As the sound waves rippled through the plasma, they created bubbles.

Around 380,000 years after the Big Bang the process stopped as the universe cooled down, freezing the shape of the bubbles.

Also Read | Cartesian coordinates: a way to find your way 

The bubbles then grew larger as the universe expanded, similar to other fossilised remnants from the time after the Big Bang.

Astronomers previously detected signals of BAOs in 2005 when looking at data from nearby galaxies.

But the newly discovered bubble is the first known single baryon acoustic oscillation, according to the researchers.

‘Unexpected’

The astronomers called their bubble Ho’oleilana — “sent murmurs of awakening” — taking the name from a Hawaiian creation chant.

The name came from the study’s lead author Brent Tully, an astronomer at the University of Hawaii.

The bubble was discovered by chance, as part of Tully’s work searching through new catalogues of galaxies.

“It was something unexpected,” Pomarede said.

Also Read | Sahara space rock 4.5 billion years old upends assumptions about the early Solar System 

Tully said in a statement that the bubble is “so huge that it spills to the edges of the sector of the sky that we were analysing”.

The pair enlisted the help of Australian cosmologist and BAO expert Cullan Howlett, who “mathematically determined the spherical structure which best corresponded to the data provided,” Pomarede said.

This allowed the trio to visualise the three-dimensional shape of Ho’oleilana — and the position of the archipelagos of galaxies inside it.

It may be the first, but more bubbles could soon be spotted across the universe.

Europe’s Euclid space telescope, which launched into July, takes in a wide view of the universe, potentially enabling it to snare some more bubbles.

Massive radio telescopes called the Square Kilometre Array, being built in South Africa and Australia, could also offer a new image of galaxies from the viewpoint of the Southern Hemisphere, Pomarede said.