JWST’s mysterious young galaxy: dead, or just sleeping?
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?
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
Key Takeaways
- All throughout the Universe, the life cycle of stars inside galaxies tells a similar story: gas clouds collapse, new stars form, and that energy feeds back into the gas, bringing an end to star-formation.
- This cycle doesn't repeat forever, however. After a large-enough star-forming event or a sufficient number of star-forming episodes, no star-forming gas remains, and a galaxy immediately becomes dead.
- Using JWST data, scientists have just discovered the earliest, farthest galaxy ever to exhibit signs of a large star-formation episode recently shutting off. Is it dead for good, or just sleeping for now?
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.
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.
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.
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.
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.
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.
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.
However, early on, particularly with smaller galaxies, transitions may have been abrupt.
This small portion of the JADES field-of-view showcases novel details that are only now available with the collaboration’s second data release. This represents one of the deepest JWST views of the distant Universe to date, and may contain some additional cosmic record-breakers that have yet to be teased out of the full suite of data. Many small, faint galaxies will hold the key to understanding how star-formation begins and ends.
It raises the question: after major star-forming episodes, do young galaxies die permanently, or will star-formation reawaken?
This galaxy, IRAS 16399, contains a megamazer located some 370 million light-years from Earth. There’s a supermassive black hole, two cores, and a massive starburst region occurring inside, with the latter giving rise to a megamaser. After a starburst, some galaxies never form stars again; in others, star-formation will reawaken in time.
At last, JWST observed a small, young galaxy that’s only recently exited a star-forming epoch.
Within the vast and impressive JADES field of view, a galaxy with only 400-600 million solar masses worth of stars has been spotted, whose light arrives just 700 million years after the Big Bang. While the stars inside this galaxy span perhaps ~3000 light-years across, star-formation proceeded in a giant burst that ended 10-20 million years prior to our observations.
This galaxy, JADES-GS-z7-01-QU, is just 700 million years old, with 400-600 million solar masses worth of stars inside.
Galaxy clusters, like Abell S740, are the largest bound structures in the Universe. When spirals merge, for example, a large number of new stars form, but either post-merger or by speeding through the intra-cluster medium, gas can be stripped away, leading to the end of star formation in that galaxy and, eventually, a red-and-dead final structure. It is possible that red-and-dead galaxies can form much earlier in the Universe’s history than current observations indicate, and JWST will be the tool that determines the answer.
It exited a major episode of star-formation just 10-20 million years ago, appearing “dead” momentarily.
The galaxy JADES-GS-z7-01-QU, shown here as imaged with JWST’s NIRCam instrument, is intrinsically blue in color, shows no evidence for new stars in 10-20 million years, but shows us this low-mass galaxy as it was just 700 million years after the Big Bang. Whether star-formation has ended in this galaxy temporarily or permanently has not been established.
Is this a permanent death, with no future star-formation episodes remaining?
A spiral galaxy typically consists of four main gaseous regions within the disk: diffuse atomic gas, dense molecular gas, stars and star clusters, and ionized regions of matter arising from energy injections from star-forming regions, young stars, and stellar cataclysms. JWST, along with the other PHANGS data sources, helps reveal different aspects of this life cycle, but once a galaxy’s gas is gone and no new gas reservoirs fall inside, star-formation ends permanently.
Or is it simply temporarily quenched, where new star-forming episodes await in the future?
An artistic representation of a starburst galaxy, where the entire galaxy itself behaves as a star-forming region, using data from the FIRE (Feedback in Realistic Environments) simulation that includes strong bursts of star-formation. For the first ~3 billion years of cosmic history, the star-formation rate rose and rose until reaching a peak, but has fallen off significantly in the ~10-11 billion years since. Whether starburst galaxies become red-and-dead or will form new stars later on depends on factors we have not yet fully understood, especially at early times.
With JWST observations, additional early, low-mass galaxies will teach us how the Universe truly grew up.
The distant galaxy MACS1149-JD1 is gravitationally lensed by a foreground cluster, allowing it to be imaged at high resolution and with multiple instruments, including Hubble and ALMA. Based on measurements of the stellar populations found inside, this object, whose light comes from when the Universe was just 530 million years old, contains stars that are at least 280 million years old within it. Like many early galaxies, it contains a supermassive black hole that suggests it arose due to the direct collapse mechanism. Gravitational lensing can reveal the most distant, faint, low-mass galaxies of all.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.
