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Dwarf galaxies use 10-million-year quiet period to churn out stars

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Dwarf galaxies use 10-million-year quiet period to churn out stars


If you look at massive galaxies teeming with stars, you might be forgiven in thinking they are star factories, churning out brilliant balls of gas. But actually, less evolved dwarf galaxies have bigger regions of star factories, with higher rates of star formation.

Now, University of Michigan researchers have discovered the reason underlying this: These galaxies enjoy a 10-million-year delay in blowing out the gas cluttering up their environments. Star-forming regions are able to hang on to their gas and dust, allowing more stars to coalesce and evolve.

In these relatively pristine dwarf galaxies, massive stars — stars about 20 to 200 times the mass of our sun — collapse into black holes instead of exploding as supernovae. But in more evolved, polluted galaxies, like our Milky Way, they are more likely to explode, thereby generating a collective superwind. Gas and dust get blasted out of the galaxy, and star formation quickly stops.

Their findings are published in the Astrophysical Journal.

“As stars go supernova, they pollute their environment by producing and releasing metals,” said Michelle Jecmen, study first author and an undergraduate researcher. “We argue that at low metallicity — galaxy environments that are relatively unpolluted — there is a 10-million-year delay in the start of strong superwinds, which, in turn, results in higher star formation.”

The U-M researchers point to what’s called the Hubble tuning fork, a diagram that depicts the way astronomer Edwin Hubble classified galaxies. In the handle of the tuning fork are the largest galaxies. Huge, round and brimming with stars, these galaxies have already turned all of their gas into stars. Along the tines of the tuning fork are spiral galaxies that do have gas and star-forming regions along their compact arms. At the end of the tuning fork’s tines are the least evolved, smallest galaxies.

“But these dwarf galaxies have just these really mondo star-forming regions,” said U-M astronomer Sally Oey, senior author of the study. “There have been some ideas around why that is, but Michelle’s finding offers a very nice explanation: These galaxies have trouble stopping their star formation because they don’t blow away their gas.”

Additionally, this 10-million-year period of quiet offers astronomers the opportunity to peer at scenarios similar to the cosmic dawn, a period of time just after the Big Bang, Jecmen said. In pristine dwarf galaxies, gas clumps together and forms gaps through which radiation can escape. This previously known phenomenon is called the “picket fence” model, with UV radiation escaping between slats in the fence. The delay explains why gas would have had time to clump together.

Ultraviolet radiation is important because it ionizes hydrogen — a process that also occurred right after the Big Bang, causing the universe to go from opaque to transparent.

“And so looking at low-metallicity dwarf galaxies with lots of UV radiation is somewhat similar to looking all the way back to the cosmic dawn,” Jecmen said. “Understanding the time near the Big Bang is so interesting. It’s foundational to our knowledge. It’s something that happened so long ago — it’s so fascinating that we can see sort of similar situations in galaxies that exist today.”

A second study, published in the Astrophysical Journal Letters and led by Oey, used the Hubble Space Telescope to look at Mrk 71, a region in a nearby dwarf galaxy about 10 million light years away. In Mrk 71, the team found observational evidence of Jecmen’s scenario. Using a new technique with the Hubble Space Telescope, the team employed a filter set that looks at the light of triply ionized carbon.

In more evolved galaxies with lots of supernova explosions, those explosions heat gas in a star cluster to very high temperatures — to millions of degrees Kelvin, Oey said. As this hot superwind expands, it blasts the rest of the gas out of the star clusters. But in low metallicity environments such as Mrk 71, where stars aren’t blowing up, energy within the region is radiated away. It doesn’t have the chance to form a superwind.

The team’s filters picked up a diffuse glow of the ionized carbon throughout Mrk 71, demonstrating that the energy is radiating away. Therefore, there is no hot superwind, instead allowing dense gas to remain throughout the environment.

Oey and Jecmen say there are many implications for their work.

“Our findings may also be important in explaining the properties of galaxies that are being seen at cosmic dawn by the James Webb Space Telescope right now,” Oey said. “I think we’re still in the process of understanding the consequences.”



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Inherited predisposition for higher muscle strength may protect against common morbidities

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Inherited predisposition for higher muscle strength may protect against common morbidities


A study conducted at the Faculty of Sport and Health Sciences at the University of Jyväskylä showed that a genetic predisposition for higher muscle strength predicts a longer lifespan and a lower risk for developing common diseases. This is the most comprehensive international study to date on hereditary muscle strength and its relationship to morbidity. The genome and health data of more than 340,000 Finns was used in the research.

Muscle strength, especially hand grip strength, can indicate an individual’s physiological resources to protect against age-related diseases and disabilities, as well as their ability to cope with them. Age-related loss of muscle strength is individual and influenced not only by lifestyle but also by genetics.

The study revealed that individuals with a genetic predisposition for higher muscle strength have a slightly lower risk for common noncommunicable diseases and premature mortality. However, it did not predict better survival after acute adverse health events compared to the time before illness onset.

“It seems that a genetic predisposition for higher muscle strength reflects more on an individual’s intrinsic ability to resist and protect oneself against pathological changes that occur during aging than the ability to recover or completely bounce back after severe adversity,” says doctoral researcher Päivi Herranen from the Faculty of Sport and Health Sciences.

The research utilized a unique study population

Muscle strength is a multifactorial trait influenced by lifestyle and environmental factors but also by numerous genetic variants, each with a very small effect on muscle strength. In this study, the genetic predisposition for muscle strength was defined by constructing a polygenic score for muscle strength, which summarizes the effects of hundreds of thousands of genetic variants into a single score. The polygenic score makes it possible to compare participants with an exceptionally high or low genetic predisposition for muscle strength, and to investigate associations with inherited muscle strength and other phenotypes, in this case, common diseases.

“In this study, we were able to utilize both genetic information and health outcomes from over 340,000 Finnish men and women,” Herranen explains.

“To our knowledge, this is the first study to investigate the association between a genetic predisposition for muscle strength and various diseases on this scale.”

Further research on the effects of lifestyles is still needed

Information about the genetic predisposition for muscle strength could be used alongside traditional risk assessment in identifying individuals who are at particularly high risk of common diseases and health adversities. However, further research on the topic is still needed.

“Based on these results, we cannot say how lifestyle factors, such as physical activity, modify an individual’s intrinsic ability to resist diseases and whether their impact on health differs among individuals due to genetics,” Herranen notes.

The study utilized the internationally unique FinnGen dataset, compiled through the collaboration of Finnish biobanks. The dataset consisted of 342,443 Finns who had given their consent and provided a biobank sample. The participants were aged 40 to 108 years, and 53% of them were women. The diagnoses selected for the study were based on the leading causes of death and the most significant noncommunicable diseases in Finland. Selected diagnoses included the most common cardiometabolic and pulmonary diseases, musculoskeletal and connective tissue diseases, falls and fractures, mental health and cognitive disorders, cancers, as well as overall mortality and mortality from cardiovascular diseases.

The study is the second publication of Päivi Herranen’s doctoral thesis, which investigates how genetics and environmental factors affect biological aging, particularly the weakening of muscle strength and functional capacity with age. The research is part of the GenActive project, funded by the Research Council of Finland and the Juho Vainio and Päivikki and Sakari Sohlberg foundations. The project is led by Assistant Professor and Academy Research Fellow Elina Sillanpää. The research was conducted in collaboration with the Gerontology Research Center (GEREC), the Institute for Molecular Medicine Finland (FIMM), and the FinnGen research project.



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Brightest gamma-ray burst of all time came from the collapse of a massive star

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Brightest gamma-ray burst of all time came from the collapse of a massive star


In October 2022, an international team of researchers, including Northwestern University astrophysicists, observed the brightest gamma-ray burst (GRB) ever recorded, GRB 221009A.

Now, a Northwestern-led team has confirmed that the phenomenon responsible for the historic burst — dubbed the B.O.A.T. (“brightest of all time”) — is the collapse and subsequent explosion of a massive star. The team discovered the explosion, or supernova, using NASA’s James Webb Space Telescope (JWST).

While this discovery solves one mystery, another mystery deepens.

The researchers speculated that evidence of heavy elements, such as platinum and gold, might reside within the newly uncovered supernova. The extensive search, however, did not find the signature that accompanies such elements. The origin of heavy elements in the universe continues to remain as one of astronomy’s biggest open questions.

The research will be published on Friday (April 12) in the journal Nature Astronomy.

“When we confirmed that the GRB was generated by the collapse of a massive star, that gave us the opportunity to test a hypothesis for how some of the heaviest elements in the universe are formed,” said Northwestern’s Peter Blanchard, who led the study. “We did not see signatures of these heavy elements, suggesting that extremely energetic GRBs like the B.O.A.T. do not produce these elements. That doesn’t mean that all GRBs do not produce them, but it’s a key piece of information as we continue to understand where these heavy elements come from. Future observations with JWST will determine if the B.O.A.T.’s ‘normal’ cousins produce these elements.”

Blanchard is a postdoctoral fellow at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), where he studies superluminous supernovae and GRBs. The study includes co-authors from the Center for Astrophysics | Harvard & Smithsonian; University of Utah; Penn State; University of California, Berkeley; Radbound University in the Netherlands; Space Telescope Science Institute; University of Arizona/Steward Observatory; University of California, Santa Barbara; Columbia University; Flatiron Institute; University of Greifswald and the University of Guelph.

Birth of the B.O.A.T.

When its light washed over Earth on Oct. 9, 2022, the B.O.A.T. was so bright that it saturated most of the world’s gamma-ray detectors. The powerful explosion occurred approximately 2.4 billion light-years away from Earth, in the direction of the constellation Sagitta and lasted a few hundred seconds in duration. As astronomers scrambled to observe the origin of this incredibly bright phenomenon, they were immediately hit with a sense of awe.

“As long as we have been able to detect GRBs, there is no question that this GRB is the brightest we have ever witnessed by a factor of 10 or more,” Wen-fai Fong, an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and member of CIERA, said at the time.

“The event produced some of the highest-energy photons ever recorded by satellites designed to detect gamma rays,” Blanchard said. “This was an event that Earth sees only once every 10,000 years. We are fortunate to live in a time when we have the technology to detect these bursts happening across the universe. It’s so exciting to observe such a rare astronomical phenomenon as the B.O.A.T. and work to understand the physics behind this exceptional event.”

A ‘normal’ supernova

Rather than observe the event immediately, Blanchard, his close collaborator Ashley Villar of Harvard University and their team wanted to view the GRB during its later phases. About six months after the GRB was initially detected, Blanchard used the JWST to examine its aftermath.

“The GRB was so bright that it obscured any potential supernova signature in the first weeks and months after the burst,” Blanchard said. “At these times, the so-called afterglow of the GRB was like the headlights of a car coming straight at you, preventing you from seeing the car itself. So, we had to wait for it to fade significantly to give us a chance of seeing the supernova.”

Blanchard used the JWST’s Near Infrared Spectrograph to observe the object’s light at infrared wavelengths. That’s when he saw the characteristic signature of elements like calcium and oxygen typically found within a supernova. Surprisingly, it wasn’t exceptionally bright — like the incredibly bright GRB that it accompanied.

“It’s not any brighter than previous supernovae,” Blanchard said. “It looks fairly normal in the context of other supernovae associated with less energetic GRBs. You might expect that the same collapsing star producing a very energetic and bright GRB would also produce a very energetic and bright supernova. But it turns out that’s not the case. We have this extremely luminous GRB, but a normal supernova.”

Missing: Heavy elements

After confirming — for the first time — the presence of the supernova, Blanchard and his collaborators then searched for evidence of heavy elements within it. Currently, astrophysicists have an incomplete picture of all the mechanisms in the universe that can produce elements heavier than iron.

The primary mechanism for producing heavy elements, the rapid neutron capture process, requires a high concentration of neutrons. So far, astrophysicists have only confirmed the production of heavy elements via this process in the merger of two neutron stars, a collision detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2017. But scientists say there must be other ways to produce these elusive materials. There are simply too many heavy elements in the universe and too few neutron-star mergers.

“There is likely another source,” Blanchard said. “It takes a very long time for binary neutron stars to merge. Two stars in a binary system first have to explode to leave behind neutron stars. Then, it can take billions and billions of years for the two neutron stars to slowly get closer and closer and finally merge. But observations of very old stars indicate that parts of the universe were enriched with heavy metals before most binary neutron stars would have had time to merge. That’s pointing us to an alternative channel.”

Astrophysicists have hypothesized that heavy elements also might be produced by the collapse of a rapidly spinning, massive star — the exact type of star that generated the B.O.A.T. Using the infrared spectrum obtained by the JWST, Blanchard studied the inner layers of the supernova, where the heavy elements should be formed.

“The exploded material of the star is opaque at early times, so you can only see the outer layers,” Blanchard said. “But once it expands and cools, it becomes transparent. Then you can see the photons coming from the inner layer of the supernova.”

“Moreover, different elements absorb and emit photons at different wavelengths, depending on their atomic structure, giving each element a unique spectral signature,” Blanchard explained. “Therefore, looking at an object’s spectrum can tell us what elements are present. Upon examining the B.O.A.T.’s spectrum, we did not see any signature of heavy elements, suggesting extreme events like GRB 221009A are not primary sources. This is crucial information as we continue to try to pin down where the heaviest elements are formed.”

Why so bright?

To tease apart the light of the supernova from that of the bright afterglow that came before it, the researchers paired the JWST data with observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile.

“Even several months after the burst was discovered, the afterglow was bright enough to contribute a lot of light in the JWST spectra,” said Tanmoy Laskar, an assistant professor of physics and astronomy at the University of Utah and a co-author on the study. “Combining data from the two telescopes helped us measure exactly how bright the afterglow was at the time of our JWST observations and allow us to carefully extract the spectrum of the supernova.”

Although astrophysicists have yet to uncover how a “normal” supernova and a record-breaking GRB were produced by the same collapsed star, Laskar said it might be related to the shape and structure of the relativistic jets. When rapidly spinning, massive stars collapse into black holes, they produce jets of material that launch at rates close to the speed of light. If these jets are narrow, they produce a more focused — and brighter — beam of light.

“It’s like focusing a flashlight’s beam into a narrow column, as opposed to a broad beam that washes across a whole wall,” Laskar said. “In fact, this was one of the narrowest jets seen for a gamma-ray burst so far, which gives us a hint as to why the afterglow appeared as bright as it did. There may be other factors responsible as well, a question that researchers will be studying for years to come.”

Additional clues also may come from future studies of the galaxy in which the B.O.A.T. occurred. “In addition to a spectrum of the B.O.A.T. itself, we also obtained a spectrum of its ‘host’ galaxy,” Blanchard said. “The spectrum shows signs of intense star formation, hinting that the birth environment of the original star may be different than previous events.”

Team member Yijia Li, a graduate student at Penn State, modeled the spectrum of the galaxy, finding that the B.O.A.T.’s host galaxy has the lowest metallicity, a measure of the abundance of elements heavier than hydrogen and helium, of all previous GRB host galaxies. “This is another unique aspect of the B.O.A.T. that may help explain its properties,” Li said.

The study, “JWST detection of a supernova associated with GRB 221009A without an r-process signature,” was supported by NASA (award number JWST-GO-2784) and the National Science Foundation (award numbers AST-2108676 and AST-2002577). This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope.



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Stellar winds of three sun-like stars detected for the first time

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Stellar winds of three sun-like stars detected for the first time


An international research team led by a researcher from the University of Vienna has for the first time directly detected stellar winds from three Sun-like stars by recording the X-ray emission from their astrospheres, and placed constraints on the mass loss rate of the stars via their stellar winds. The study is currently published in Nature Astronomy.

Astrospheres, stellar analogues of the heliosphere that surrounds our solar system, are very hot plasma bubbles blown by stellar winds into the interstellar medium, a space filled with gas and dust. The study of the stellar winds of low-mass stars similar to the Sun allows us to understand stellar and planetary evolution, and ultimately the history and future of our own star and solar system. Stellar winds drive many processes that evaporate planetary atmospheres into space and therefore lead to atmospheric mass loss.

Although escape rates of planets over an hour or even a year are tiny, they operate over long geological periods. The losses accumulate and can be a decisive factor for a planet evolving into a habitable world or an airless rock. Despite their importance for the evolution of both stars and planets, winds of Sun-like stars are notoriously difficult to constrain. Mainly composed of protons and electrons, they also contain a small quantity of heavier highly charged ions (e.g. oxygen, carbon). It is these ions which, by capturing electrons from the neutrals of the interstellar medium around the star, emit X-rays.

X-ray emission from astropheres detected

An international research team led by Kristina Kislyakova, Senior Scientist at the Department of Astrophysics of the University of Vienna, has detected for the first time the X-ray emission from the astrospheres around three sun-like stars, so called main sequence stars which are stars in the prime of their life, and has thus recorded such winds for the first time directly, allowing them to place constraints on the mass loss rate of the stars via their stellar winds.

These results, based on observations with the XMM-Newton space telescope, are currently published in Nature Astronomy. The researchers observed the spectral fingerprints (so-called spectral lines) of the oxygen ions with XMM-Newton and were able to determine the quantity of oxygen and ultimately the total mass of stellar wind emitted by the stars. For the three stars with detected astrospheres, named 70 Ophiuchi, epsilon Eridani, and 61 Cygni, the researchers estimated their mass loss rates to be 66.5±11.1, 15.6±4.4, and 9.6±4.1 times the solar mass loss rate, respectively. This means that the winds from these stars are much stronger than the solar wind, which might be explained by stronger magnetic activity of these stars.

“In the solar system, solar wind charge exchange emission has been observed from planets, comets, and the heliosphere and provides a natural laboratory to study the solar wind’s composition,” explains the lead author of the study, Kristina Kislyakova. “Observing this emission from distant stars is much more tricky due to the faintness of the signal. In addition to that, the distance to the stars makes it very difficult to disentangle the signal emitted by the astrosphere from the actual X-ray emission of the star itself, part of which is “spread” over the field-of-view of the telescope due to instrumental effects. We have developed a new algorithm to disentangle the stellar and the astrospheric contributions to the emission and detected charge exchange signals originating from stellar wind oxygen ions and the surrounding neutral interstellar medium of three main-sequence stars. This has been the first time X-ray charge exchange emission from astrospheres of such stars has been detected. Our estimated mass loss rates can be used as a benchmark for stellar wind models and expand our limited observational evidence for the winds of Sun-like stars.”

Co-author Manuel Güdel, also of the University of Vienna, adds, “there have been world-wide efforts over three decades to substantiate the presence of winds around Sun-like stars and measure their strengths, but so far only indirect evidence based on their secondary effects on the star or its environment alluded to the existence of such winds; our group previously tried to detect radio emission from the winds but could only place upper limits to the wind strengths while not detecting the winds themselves. Our new X-ray based results pave the way to finding and even imaging these winds directly and studying their interactions with surrounding planets.”

“In the future, this method of direct detection of stellar winds in X-rays will be facilitated thanks to future high resolution instruments, like the X-IFU spectrometer of the European Athena mission. The high spectral resolution of X-IFU will resolve the finer structure and emission ratio of the oxygen lines (as well as other fainter lines), that are hard to distinguish with XMM’s CCD resolution, and provide additional constraints on the emission mechanism; thermal emission from the stars, or non-thermal charge exchange from the astrospheres.” — explains CNRS researcher Dimitra Koutroumpa, a co-author of the study.



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