All posts tagged: star formation

Dark matter and star clusters work together to reshape the centers of galaxies

Dark matter and star clusters work together to reshape the centers of galaxies

Published by Jenni Sidey

A galaxy simulation shows that nuclear star clusters and nuclear stellar disks can grow together as a stellar bar funnels gas toward the galactic center. Repeated shocks from stellar feedback move gas inward and trigger new star formation, while the surrounding nuclear disk gradually expands from the inside out. The connection can become difficult to recognize as the two structures evolve at different rates, and mergers with massive star clusters can further reshape the galactic center. At the heart of a barred galaxy, two stellar structures can grow around the same central region. One is compact and pressure-supported. The other spreads outward as a rotating disk. Their apparent disconnect has obscured a shared origin. A simulation from the SMUGGLE-Ring project shows how both structures can emerge together in a Milky Way-mass galaxy. It examines nuclear star clusters, or NSCs, and nuclear stellar disks, or NSDs. Observational surveys have found no clear correlation between their masses and sizes, reinforcing the idea that they form separately. The work follows their development over four billion years. A stellar …

New Gaia data is challenging a 50-year-old assumption about how stars and galaxies form

New Gaia data is challenging a 50-year-old assumption about how stars and galaxies form

Published by Jenni Sidey

Astronomers found that star clusters do not always form the same balance of small and large stars, challenging a long-standing assumption used to measure galaxies. Gaia data show that a key dividing point in stellar masses changes with cluster age, matching models in which star-forming conditions influence which stars are born. The result could change estimates of galaxy mass and star formation, especially for very distant galaxies observed by the James Webb Space Telescope. For more than half a century, astronomers have relied on a basic rule to estimate the stars they cannot see. New evidence from Milky Way star clusters suggests that rule is not universal, with consequences for how distant galaxies are weighed. The rule is called the initial mass function, or IMF. It describes how many stars of different masses are born together. Because faint, low-mass stars are difficult to detect in distant galaxies, astronomers infer their numbers from brighter, heavier stars. University of Missouri researchers found that the balance between low- and high-mass stars can change from one stellar environment to …

Andromeda’s star formation has been slowing down for 500 million years

Andromeda’s star formation has been slowing down for 500 million years

Published by Jenni Sidey

Andromeda has been forming fewer stars for about 500 million years, with an especially sharp drop recently. Most of the slowdown comes from declining activity in a huge ring where much of the galaxy’s new star formation occurs. A nearby small galaxy called M32 may have influenced one quieter region, but astronomers cannot yet confirm that connection. Andromeda has not stopped making stars, but its busiest stellar nursery is losing momentum. A Hubble Space Telescope census shows that the nearby galaxy’s star formation has declined for about 500 million years, then dropped even faster during the past 40 million. The analysis combines two major Hubble surveys that mapped roughly two-thirds of Andromeda’s star-forming disk. Together, the Panchromatic Hubble Andromeda Treasury and its southern counterpart measured about 200 million individual stars. That scale matters because stars preserve a galaxy’s history. Their colors, brightness, and masses reveal when different regions were actively producing new suns. “We need to measure the individual stars because they are the fossil record of the galaxy’s formation. Hubble is the only telescope …

New study challenges existing knowledge for why galaxies stop forming stars

New study challenges existing knowledge for why galaxies stop forming stars

Published by Jenni Sidey

Most galaxy collisions do not cause galaxies to stop making new stars. A galaxy’s central black hole and its slow, long-term growth appear more important than sudden cosmic crashes. The findings suggest galaxies usually fade gradually because they lose access to fresh gas, rather than shutting down after one violent event. Galaxy mergers have carried a dramatic reputation for decades. Two enormous systems collide, gas rushes inward, a central black hole erupts and star formation ends. A sweeping simulation analysis now challenges nearly every step of that familiar story. Researchers at Florida International University examined 11,724 simulated galaxies and found that mergers were neither necessary nor sufficient to stop star formation. The shutdown process, known as quenching, appeared far more closely tied to gradual internal evolution. Only about 3 percent of major mergers were associated with quenching within a window beginning one billion years before the shutdown process. Extending that window to two billion years raised the figure to about 5 percent. When the team included mergers of every size, the proportions rose to about …

Radio observations reveal once hidden structures around the Orion Nebula

Radio observations reveal once hidden structures around the Orion Nebula

Published by Jenni Sidey

Orion is about as familiar as a patch of sky gets. Visible without a telescope, studied by nearly every major instrument ever pointed at the heavens, mapped and catalogued across centuries of astronomy. What could possibly be left to find? Quite a lot, it turns out. An international team led by Juan Diego Soler at the University of Vienna has produced the sharpest maps ever made of neutral atomic hydrogen in the Orion Nebula. The images look nothing like what the standard picture predicted. Expanding shells, previously invisible cavities, and a mysterious elongated structure of gas jutting outward from the main bubble—none of it was there in older observations. Moreover, the mass of the whole surrounding shell, which previous studies put at roughly one thousand times that of the Sun, now appears to be nearly ten times lower. That is not a small correction. It rewrites something fundamental about how efficiently young massive stars reshape the space around them. Juan Diego Soler at the University of Vienna. (CREDIT: Juan Diego Soler) The Gas You Cannot …

Organic molecules can survive violent supernova explosions – fueling star and planet formation

Organic molecules can survive violent supernova explosions – fueling star and planet formation

Published by Jenni Sidey

A supernova remnant is supposed to be a rough neighborhood for a newborn star. Shock waves rip through space at thousands of kilometers per second. Cosmic rays and X-rays flood nearby gas. Rare elements get tossed into the surrounding clouds. Yet inside one of these violent leftovers, astronomers have found something unexpectedly delicate still holding together. Using the Atacama Large Millimeter/submillimeter Array, or ALMA, a team in Japan identified two warm, dense cocoons of gas around infant stars inside the supernova remnant RX J1713.7−3946. These objects, known as hot cores, are rich in molecules linked to the chemistry of star and planet formation. According to the team, this is the first time hot cores have been detected inside a supernova remnant. The finding, published in The Astrophysical Journal, suggests that even after a massive nearby star explodes, some newborn stars may stay wrapped tightly enough in their natal material to protect a surprisingly rich chemical inventory. Artist’s impression of hot cores —warm cradles of molecular gas surrounding a newborn star—discovered within a supernova remnant. Blue …

JWST reveals why some distant galaxies suddenly stop forming stars

JWST reveals why some distant galaxies suddenly stop forming stars

Published by Jenni Sidey

Distant galaxies that abruptly stopped making stars have puzzled astronomers for years. About 9 billion years ago, during one of the busiest periods in cosmic history, many massive galaxies were still building stars at a furious pace. Yet a smaller group had already slammed on the brakes. New observations from the James Webb Space Telescope suggest that, in many cases, those sudden shutdowns were not gentle. Instead, they may have followed violent collisions. These collisions left behind compact, disturbed remnants. The work, led by researchers at the University of Nottingham and published in Monthly Notices of the Royal Astronomical Society, examined a large sample of recently quenched galaxies. These are systems that had rapidly stopped forming stars and were caught in transition. Those galaxies are valuable because they offer a snapshot of what happens near the moment when star formation switches off. “This was the epoch of peak activity in the Universe, when many of the most massive galaxies we see today were formed,” said Professor Omar Almaini, who led the team behind the study. …

Astronomers detect first direct evidence of star-forming gas in early galaxies

Astronomers detect first direct evidence of star-forming gas in early galaxies

Published by Jenni Sidey

The first galaxies were already busy by the time the universe was 700 to 800 million years old. Stars were forming fast. Structures were taking shape. Additionally, huge stores of gas were feeding that growth. What astronomers have struggled to see clearly is the neutral gas at the center of that process. It is the cooler material that directly supplies star formation. That missing piece has now come into view. An international team led by Assistant Professor Yoshinobu Fudamoto and Professor Masamune Oguri of Chiba University used the Atacama Large Millimeter/submillimeter Array, or ALMA, to detect the [O I] 145 micrometer emission line in four distant galaxies. The signal comes from neutral oxygen and serves as a direct tracer of neutral gas. As a result, it is a powerful way to study the material that fuels early star formation. The galaxies were seen as they existed more than 13 billion years ago, at redshifts above 6.5. According to the team, this is the most distant direct detection yet of neutral gas in typical star-forming galaxies. …

Hubble and JWST reveal thousands of young star clusters emerging from their birth clouds

Hubble and JWST reveal thousands of young star clusters emerging from their birth clouds

Published by Jenni Sidey

A young star cluster does not begin life in the open. It starts buried inside thick clouds of gas and dust, hidden from ordinary view while newborn stars heat, ionize, and push against the material around them. Now, observations from the Hubble and James Webb space telescopes suggest that the biggest clusters do not stay hidden for long. In four nearby galaxies, astronomers found that more massive young star clusters clear away their birth clouds faster than smaller ones do. That means the brightest, most energetic clusters can begin flooding their host galaxies with radiation sooner, with consequences that reach from galaxy evolution to planet formation. “I was excited to see that the emerging timescale of a star cluster is related to its mass in stars. This has implications on a range of research fields, from planet formation to galaxy evolution”, said Alex Pedrini, a PhD student at Stockholm University’s Department of Astronomy and the first and corresponding author of the study. The work, published in Nature Astronomy, draws on a large census of roughly …

For the first time, astronomers identify the edge of the Milky Way’s disc

For the first time, astronomers identify the edge of the Milky Way’s disc

Published by Jenni Sidey

The Milky Way does not come with a clean outer line. Its disc does not stop the way a coastline does. It fades, becoming harder and harder to define as stars grow sparse and the structure stretches into the dark. That uncertainty has made one question especially stubborn for astronomers: where does the galaxy’s star-forming disc actually end? A new analysis points to an answer. By tracing the ages of stars across the Milky Way, an international team of astronomers found that most of the galaxy’s star formation is confined to a region within about 40,000 light-years of the Galactic Centre. Past that point, the pattern of stellar ages shifts in a way that suggests the main star-forming disc has already run out. According to Dr. Karl Fiteni from the University of Insubria, “The extent of the Milky Way’s star-forming disc has long been an open question in Galactic archaeology. By mapping how stellar ages change across the disc, we now have a clear, quantitative answer.” Inside the star-forming disc abundant cold gas fuels star …