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JWST detects oldest ‘dead’ galaxy in the known universe — and its death could defy cosmology

Tuesday April 9, 2024 12:34 pm

Astronomers using the JWST have detected the oldest “dead” galaxy ever detected, at just 700 million years after the Big Bang. The stalled-out relic flouts explanation by our current understanding of the early cosmos.

 Astronomers using JWST (the James Webb Space Telescope) have discovered the oldest “dead” galaxy ever seen — but the cosmic carcass has left scientists baffled as it disregards explanation by our current knowledge of the early cosmos. The galaxy abruptly and mysteriously stopped star formation when the cosmos was just 700 million years old, when innumerable stars were birthing elsewhere in the universe due to an abundance of pristine gas and dust.

The galaxy, christened JADES-GS-z7-01-QU and described in a paper published in the journal Nature on Wednesday (March 6, 2024), provides astrophysicists with a peek into the elusive underpinnings of galaxy evolution in a primeval universe, including why galaxies halt forming new stars and whether forces behind their starbursts alter across epochs.

“Galaxies need a rich supply of gas to form new stars, and the early universe was like an all-you-can-eat buffet,” study lead author Tobias Looser (a researcher at the University of Cambridge’s Kavli Institute for Cosmology), said in a statement. Current models cannot explain how this newfound galaxy not only took shape in less than a billion years post the Big Bang, but also shut down its star factory so hurriedly. “It’s only later in the universe that we [usually] start to see galaxies stop forming stars,” study co-author Francesco D’Eugenio, also a researcher at University of Cambridge’s Kavli Institute for Cosmology, said in the statement. In contrast, a handful of other “dead” galaxies found elsewhere appear to have stopped forming new stars when the cosmos was about 3 billion years old, the researchers said.

“Everything seems to happen faster and more dramatically in the early universe,” added Looser. “And that might include galaxies moving from a star-forming phase to dormant or quenched.” To unearth JADES-GS-z7-01-QU, Looser and his colleagues employed the James Webb Space Telescope’s powerful infrared vision to peer through the thick veil of dust obscuring the earliest substances in the universe. Apart from being the oldest “dead” or “quenched” galaxy spotted so far, the newfound galaxy is also several times lighter than other similarly dormant galaxies previously found in the early universe.

JWST’s data suggest the galaxy strongly formed stars for anywhere between 30 million to 90 million years before it hurriedly shut off, although exactly what ended it is still unknown. A couple of different factors that can slow down or extinguish star formation are known to astronomers. For example, turbulence inside a galaxy, like radiation emitted by a supermassive black hole (SMBH), can push gas out of the galaxy and starve it of the gas reservoir it depends on to form stars.

What concluded the ‘dark ages’ in the early universe? New Webb data has just gotten us nearer to solving the mystery

Wednesday March 27, 2024 11:57 am

About 400,000 years post the Big Bang, the universe was a very dark place. The glow of the cosmos’s explosive birth had cooled, and space was packed with dense gas – mostly hydrogen – with no sources of light. Gradually, over hundreds of millions of years, the gas was drawn into clumps by gravity, and finally the clumps grew big enough to ignite. These were the earliest stars. Initially their light didn’t travel too far, as most of it was absorbed by a fog of hydrogen gas. Nevertheless, as more and more stars formed, they produced sufficient light to burn away the fog by “reionising” the gas – fashioning the transparent universe dotted with wonderful points of light we see today.

But precisely which stars produced the light that concluded the dark ages and prompted this so-called “epoch of reionisation”? Researchers have used a gargantuan cluster of galaxies as a magnifying glass to stare at faint relics of the time – and learnt that stars in small, faint dwarf galaxies were likely behind this cosmic-scale transformation.

What concluded the dark ages?

Most astronomers were already in agreement that galaxies were the main force in reionising the cosmos, but it wasn’t known how exactly they did it. We are aware that stars in galaxies should make a lot of ionising photons, but these photons need to escape the gas and dust inside their own galaxy to ionise hydrogen between galaxies. It hasn’t been known what kind of galaxies would be capable of producing and emitting enough photons to get the job done. There are two separate camps among supporters of the galaxy theory.

  • The first camp thinks huge, colossal galaxies produced the ionising photons. There were not many of these galaxies present in the early universe, but each one produced quite a bit of light. So if a certain fraction of that light succeeded to escape, it might have been adequate to reionise the universe.
  • The second camp beleives we are better off ignoring the massive galaxies and concentrating on the huge number of much smaller dwarf galaxies in the early universe. Each one of these would have produced considerably less ionising light, but with the sheer weight of their numbers they could have driven the epoch of reionisation.

A magnifying glass 4 million lightyears wide

Attempting to look at anything in the early universe is very tough. The colossal galaxies are rare, so they are tough to find. Smaller galaxies are far more common but they are too faint, which makes it hard (and expensive) to get high-quality data. To fulfil the desire to look at some of the faintest galaxies around, researchers used a huge group of galaxies termed Pandora’s Cluster as a magnifying glass. The gargantuan mass of the cluster distorts space and time, magnifying the light from objects behind it.

The bright glow of hydrogen

Researchers chose some sources which were about 0.5% of the brightness of our Milky Way and checked them for the telltale glow of ionised hydrogen. These galaxies are so very faint they were only visible thanks to the magnifying effect of Pandora’s Cluster. Observations of the researchers confirmed that these small dwarf galaxies did in fact exist in the very early universe. What’s more, it was confirmed they produced around four times as much ionising light as was considered “normal”. As these galaxies produced so much ionising light, only a small fraction of it would have needed to escape to reionise the universe.

Dwarf galaxies could have played a very large role in reionisation

Previously, researchers believed that around 20% of all ionising photons would need to escape from these smaller dwarf galaxies if they are to be the overriding contributor to reionisation. New data suggests even 5% would be adequate. So now we can assuredly say these smaller dwarf galaxies could have played a very dominant role in the epoch of reionisation.

How long will life persevere in our Cosmos?

Wednesday March 27, 2024 11:55 am

One of the most mortifying aspects of our Cosmos is the knowledge that all things will eventually pass away. New stars and stellar systems, although are likely to keep forming for many billions or even trillions of years to come, their rate of formation is on the decline, with the present star-formation rate only about 3% of what it was at its extreme some 11 billion years ago. Planets like Earth orbiting around stars like the Sun, while pretty common today, will be awfully rare in the far future. And the longest-lived stars, even if they possess Earth-sized planets around them, might be poor candidates for supporting life because of their extraordinarily active behavior.

At certain point in the far future, the last living world in the Universe will meet its demise, signaling an end to what we know as biological activity within our universe. But when in fact will this occur? And when and where will the last likelihoods for intelligent life persevere? That’s what most of us want to know.

When we attempt to put the pieces of the puzzle together, the following opportunities for life are presented:

  • For the stars that already exist, the lowest-mass ones will become livable only after hundreds of billions or even trillions of years have passed, and may remain livable for up to ~1014 (100 trillion) years.
  • For the stars that haven’t taken shape yet, it’s possible that new star-formation will bring with it new opportunities for life, extending up to ~1017 (100 quadrillion) years into the future.
  • And for the stars that will ultimately form from the mergers of brown dwarfs, they may continue igniting for up to 1021 (one sextillion) years into the future, before gravitational interactions eliminate what we think of as “galaxies” from the picture completely.

All of this comes along with a considerable extent of uncertainty and unknowns. After all, Earth, even today, remains the only world known to us where life has ever arisen and continues or has discontinued to thrive. The prospects for life, at least as we understand it, remain diverse and ubiquitous, and should be probable even far into our Universe’s cosmic future, even if our cosmic home doesn’t remain habitable for much longer. In a Universe with so many biochemical possibilities and so many worlds — past, present, and future — it would be stupid to assume that the way things unfolded here on earth represent the only reasonable pathway to successful arising of life.

Ingredients for a habitable planet

If you desire to have life arise in the Cosmos, a planet (or world, in the case of a livable moon, for instance) might not be absolutely necessary, but it is necessary that the cosmos provides a great environment where life’s emergence is welcomed by a slew of friendly conditions. That means that some amount of chemical enrichment — i.e., a great enough fraction of elements weightier than hydrogen or helium — required to have been created before the formation of the star and stellar system you’re looking at. In 2022, the total confirmed exoplanet count passed 5000 for the first time ever, and an amazing set of facts arose by analyzing which stars had planets around them at all:

  • nearly all of the planets, 98.2% of them, were present around stars that had no less than 25% of the heavy element content present in the Sun,
  • the rest 1.8% of the planets were present around stars that had between 5% and 25% of the Sun’s heavy element content,
  • and that no planets at all were discovered around stars with fewer than 5% of the heavy elements content present in the Sun.

If you desire to have a rocky world that gives life a home for surviving and thriving, presence of enough heavy elements is needed, and that places limits on where, in the evolved galaxies throughout the contemporary Universe, such planets are capable of forming.

Stars and habitability

Planets afford the raw elements from which biochemical reactions for life become possible, but another required ingredient for life’s advent is a source of energy. While a star might not be the only option for providing such a source — we are well aware that the Sun provides the energy that powers almost all forms of life on Earth. Choosing to have a star power the life on a world, however, places enormous restrictions on the types of life-friendly worlds that can arise.

A monster black hole is powering the brightest known object in the universe

Thursday March 21, 2024 9:38 am

Astronomers have discovered a quasar 12 billion light years away hosting a SMBH (supermassive black hole) that gobbles up mass more than the mass of our sun every day

A quasar 500 trillion times brighter than our sun has grabbed the tag of the brightest known object in the universe. It seems to be powered by a SMBH that is consuming a sun-sized amount of mass every day.

What are quasars?

Quasars are galactic cores where dust and gas sinking into a SMBH release energy in the form of electromagnetic radiation. Christian Wolf of the Australian National University, Canberra and his colleagues spotted the new brightest quasar called J0529-4351 for the first time in 2022 by scouring through data from the Gaia space telescope and hunting for extremely bright objects outside the Milky Way that were misidentified as stars.

Follow up observations from the Very Large Telescope (VLT) in Chile helped too

After studying follow up observations from the Very Large Telescope (VLT) in Chile, they have now concluded that J0529-4351 is the most luminous object in the universe that we know of. Wolf and his colleagues employed a device on the VLT called a spectrometer to analyze the light coming from the new brightest quasar and determine how much was produced by the SMBH’s swirling disc of gas and matter, termed its accretion disc.

Utilizing the light spectra, the scientists also estimated that the mass of the black hole was between 5 billion and 50 billion solar masses. Wolf and his colleagues also have the credit of finding the previous brightest quasar, which was about half the brightness of J0529-4351, way back in 2018. Wolf believes that the new discovery is likely to remain the record-holder for quite some time, as the vast majority of the observable sky has already been surveyed in great detail, thanks to comprehensive star catalogues such as that produced by Gaia. “This is the biggest unicorn with the longest horn on its head that we’ve found. I don’t think we’re going to top that record,” says Wolf.

The quasar’s accretion disc seems to be the widest yet discovered, at 7 light years across. This presents a rare opportunity to image the black hole directly and precisely measure its mass, says Christine Done (Durham University, UK). “This is big enough and bright enough that we could resolve it with our current instruments,” says Done. “So we could have a much more direct measure of the black hole mass in this monster, and that’s what I did get quite excited about.”

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