SCIENCE

JWST’s mysterious young galaxy: dead, or just sleeping? | by Ethan Siegel | Starts With A Bang! | Mar, 2024

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The “dead” galaxy JADES-GS-z7–01-QU, whose light comes to us from just 700 million years after the Big Bang, is low in mass and small in size. We do not yet know whether star-formation has temporarily turned off in this galaxy about 10–20 million years ago, or whether it has ended completely and permanently. Either way, this is now the youngest, earliest “dead” galaxy ever discovered, but it may merely be sleeping. (Credit: JADES Collaboration)

Given enough time, all galaxies will expel their star-forming material and wind up dead. Is this the earliest one, or is it just asleep?

All across the Universe, star birth and galactic death are linked.

The low-mass, dusty, irregular galaxy NGC 3077 is actively forming new stars, has a very blue center, and has a hydrogen gas bridge connecting it to the nearby, more massive M81. As one of 34 galaxies in the M81 Group, it’s an example of the most common type of galaxy in the Universe: much smaller and lower in mass, but far more numerous, than galaxies like our Milky Way. The young stars within it have formed from gas reservoirs still present within this galaxy, indicating an “alive” galaxy. (Credit: ESA/Hubble and NASA)

New stars can only form when cold reservoirs of gas collapse.

The Pillars of Creation are some of the last remaining dense knots of neutral, star-forming matter inside the Eagle Nebula. From the outside, hot stars irradiate the pillars, boiling the gas away. Inside the pillars, matter collapses and new stars form, which also irradiate the pillars from the inside. We are bearing witness to the last gasps of star-formation inside this region. (Credit: Roi Levi & Mike Selbi/Wikimedia Commons)

Those newborn stars, however, create violence: winds, radiation, and outflows.

Galaxies undergoing massive bursts of star formation expel large quantities of matter at great speeds. They also glow red, covering the whole galaxy, thanks to hydrogen emissions. This particular galaxy, M82, the Cigar Galaxy, is gravitationally interacting with its neighbor, M81, causing this burst of activity. Although the winds and ejecta are copious, this episode is not expected to completely “kill” the galaxy, as some gas will still persist after this episode completes. (Credits: NASA, ESA and the Hubble Heritage Team (STScI/AURA); Acknowledgment: J. Gallagher (University of Wisconsin), M. Mountain (STScI) and P. Puxley (National Science Foundation))

Those energetic emissions evaporate the surrounding material, terminating these star-forming episodes.

The near-infrared view of the Tarantula Nebula taken with JWST is higher in resolution and broader in wavelength coverage than any previous view. It heavily expands on what Hubble taught us, and this wide-field view of our neighbor galaxy, the LMC, still showcases just 0.003778 square degrees in the sky. It would take 10.9 million images of this size to cover the entire sky. The super star cluster to the right of center, R136, is the largest, most massive new star cluster found within our entire Local Group of galaxies, and has already blown a huge cavity in the gas that led to its formation. (Credit: NASA, ESA, CSA, STScI, Webb ERO Production Team)

In extreme cases, 100% of a galaxy’s gas gets expelled, creating a “dead” galaxy.

This nearby galaxy, NGC 1277, although it may appear similar to other typical galaxies found in the Universe, is remarkable for being composed primarily of older stars. Both its intrinsic stellar population and its globular clusters are all very red in color, indicating that it hasn’t formed new stars in ~10 billion years. When all of the gas within a galaxy is expelled and no new gas enters, that galaxy becomes permanently “red and dead,” as no new populations of stars can form within it. (Credit: NASA, ESA, and M. Beasley (Instituto de Astrofísica de Canarias))

While the already-created stars will persist, subsequent star-formation episodes are impossible without gas reservoirs.

This portion of Hubble’s image of the Cosmic Reef highlights the densest, dustiest region of gas and dust. New stars are being formed inside, and the cyan colored “wisps” highlight doubly-ionized oxygen, which indicates temperatures in excess of 50,000 K. When the last of the gas in this region has been blown away, no new stars will form. However, if the gas isn’t completely expelled from the galaxy, it may yet recollapse and form new stars someday. (Credit: NASA, ESA and STScI)

Modern galaxies transition slowly from active star-forming phases to passive phases.

When major mergers of similarly-sized galaxies occur in the Universe, they form new stars out of the hydrogen and helium gas present within them. This can result in severely increased rates of star-formation, similar to what we observe inside the nearby galaxy Henize 2–10, located 30 million light years away. This galaxy will likely evolve, post-merger, into another disk galaxy if copious amounts of gas remains within it, or into an elliptical if all or nearly all of the gas is expelled by the current starburst. (Credit: NASA, ESA, Zachary Schutte (XGI), Amy Reines (XGI); Processing: Alyssa Pagan (STScI))

However, early on, particularly with smaller galaxies, transitions may have been abrupt.

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