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kilopower nasa

Nuclear reactor for crewed outposts on Mars and Moon could be ready by 2022

A new type of nuclear reactor has been designed to power outposts on Moon and Mars and it could be ready for its first in-space trial within a few years. The next step is a flight test for Kilopower experimental fission reactor which completed a series of ground tests from 2007 to 2018. Patrick McClure, Kilopower project lead at the Los Alamos National Laboratory said that Kilopower should be ready by 2022 although no off-earth demonstration has been scheduled yet.

He added that three years is a doable time frame which is not NASA’s stand who has been developing the project in collaboration with DOE. NASA’s Voyager 1 and Voyager 2 probes along with Curiosity Mars rover and New Horizons spacecraft employ radioisotope thermoelectric generators which convert the heat produced by the radioactive decay of plutonium-238 into electricity. RTGs produce relatively low power. It produces nearly 110 watts of electricity in Curiosity and the upcoming Mars 2020 rover.

A crewed outpost on Mars has higher energy demands around 40 kilowatts even for a small research envisioned by NASA for the late 2030s. Electricity will be required for water purification, oxygen generation for carbon-dioxide dominated atmosphere, charging up rovers, etc. Kilopower is a fission reactor and generates heat by splitting atoms into electricity through Sterling engines. The reactor was able to successfully convert 30% of the fission heat into electricity compared to 7% of regular RTG’s in a ground test series known as KRUSTY (Kilopower Reactor Using Sterling Technology). The project started in 2015 but the basic concepts were proved back in 2012 via an experiment called Demonstration Using Flattop Fissions (DUFF). KRUSTY and DUFF are characters in the Simpsons animated universe.

The reactor is designed to produce an output of 1 kilowatt of electrical power and can be scaled up to 10 kilowatts. NASA would need 4 of such reactors including one spare reactor. The 10-kilowatt machines would be just 11 feet in height and weigh close to 2000 kilograms. Without the astronaut shielding, it would weigh close to 1500 kilograms which would mean burying it in the ground.

The reactors are quite safe and there is no threat of radiation exposure if the rocket crashes back on Earth. The reactor is a self-regulating one if it gets too hot, the Stirling engines draw more heat away from uranium core and if temperature drops, the core naturally contracts which trap more neutrons and more splitting collisions. The device will need to dump a lot of heat on Mars due to the conversion efficiency of 30% will mean 70% of the heat will remain. It will come equipped with radiators.

A potential moon lander was the first task given to them as a demonstration mission for Kilopower but the concept will not end up flying as it targeted the lunar North pole and NASA was interested in the South Pole. Kilopower is the first fission reactor concept developed in the US in the last 40 years and is surely a milestone. US had previously launched reactors in experimental satellite, SNAP-10A in April 1965 but had to shut down after just 43 days. Although the Soviet Union was able to launch more than 30 fission reactors aboard satellites from 1967 to late 1980s.

Dusty cloud G2 passes the supermassive black hole

Mysterious flare emitted by the supermassive black hole of our galaxy

The supermassive black hole present at the centre of the Milky Way, Sagittarius A* has a low activity level most of the time as it is quiet, does not possess an active nucleus and has minimum brightness fluctuations. However recently, astronomers observed that its brightness increased 75 times before it went back to normal levels. 

Tuan Do, an astronomer at University of California Los Angeles said he was both surprised and excited to observe this. He even mistook it to be the star S0-2 for its brightness. Scientists have been trying to find out what is the reason behind this event. Their observations are accepted in The Astrophysical Journal Letters and can be found here


The galactic centre was observed by Do and his team with the help of WM Keck Observatory located in Hawaii. This unusual brightening was observed on May 13 for a period of two hours that was converted into a time-lapse of a few seconds. Although black holes themselves do not emit any radiation which can be detected by the instruments, the surrounding gases emit radiation due to the friction generated by the gravitational forces of the black hole. The radiation is observed as brightness when viewed in the infrared range of the telescope. When the surroundings of the black hole glow brightly it indicates that the black hole’s gravity has captured something.

The first frame of the observation is brightest indicating that the black hole might have been brighter however it was not known that any object was approaching closer to be swallowed. There are two possible situations. An object initially considered as a gas cloud, G2 was within 36 light hours of Sagittarius A* in 2014. Being a gas cloud, it would have been shredded by the black hole however this did not occur. It was later classified as a “cosmic fizzle”. 

Another possibility is that when the star S0-2 passed close to the black hole, it might have changed the pattern of gas flow into the black hole generating more variations. Having more data is the only way of confirmation, more observations are being made by the Keck Observatory as long as the centre of the galaxy is visible from Earth. Several other telescopes have also been observing the galactic centre which includes Chandra and Spitzer space telescopes. The data could help in understanding more aspects behind the change of brightness. Scientists are eagerly awaiting the results to have a better understanding.

Journal Reference: arxiv 


Researchers detect radioactive interstellar dust in the Antarctic Ice

In new research, scientists have found evidence of dust from a nearby supernova under several thousand pounds of Antarctic snow. Our solar system not only comprises of celestial objects such as planets, moon, sun but also a lot of dust that might have originated from the interstellar sources. A group of researchers in Germany, Austria and Australia is in the search of the presence of dust on Earth to understand the circumstances in which the solar system is moving forward. The study has been published in the Physical Review Letters. 

Dominik Koll, first author of the study and a PhD candidate from Australian National University mentioned he is very excited to learn about the stellar explosions and structures present around our planet which have faraway origins. Scientists transported fresh snow which is not more than 20 years old, weighing almost 1100 pounds from the Kohnen Station located in Antarctica to Munich, Germany.

Then the snow was melted in the laboratory, filtered and evaporated for collecting dust and other micrometeorites. Dust was incinerated and put into Accelerator Mass Spectrometer. It is used to create charged ions from the sample, pass through the magnet and then into a particle accelerator before finally sending to a detector. This technique is useful for collecting only specific atomic isotopes. 

The team wanted to find iron-60, a radioactive isotope released by the supernova. It can also have other sources such as the matter irradiated by the cosmic rays. For guaranteeing it to be interstellar dust, researchers also searched for manganese-53 and compared the ratio of iron-60 to manganese-53 to the ratio expected if there was no presence of interstellar dust. A lot more iron-60 was found than expected from the cosmic rays. 

Thomas Faestermann, TU Munich explained that it was previously established that iron-60 was deposited in the solar system by a nearby supernova in the past 1.5 to 3 million years. Its prolonged presence on Earth indicates it is coming from a remaining dust cloud from a supernova.

These studies show better conditions of the interstellar environment through which Sun is travelling. It has been detected that the Sun is in a “Local Bubble” where the density of the interstellar medium is quite less than average possibly due to a recent supernova. It contains the Local Interstellar Cloud which has a higher density than the Bubble. We can know more about these regions from the dust found in Antarctica. 

There are lots of findings remaining as the Antarctic ice could lead an exposition of the history of an ancient supernova. 

Journal Reference: Physical Review Letters. 

Massive Galaxy Formation

Researchers create Universe Machine to understand the formation and evolution of galaxies

The science behind the formation of galaxies and their evolution has remained a puzzle for decades, but the answer might be found soon with the help of simulations carried using supercomputers by a group of scientists from the University of Arizona.

Observation of galaxies can only provide their snapshots over time however understanding their evolution requires computer simulations. Astronomers have used this technique for testing different theories of the formation of galaxies. Peter Behroozi, an assistant professor at the UA Steward Observatory generated millions of universes on a supercomputer, each having different physical theories on the formation of galaxies. The paper has been published in Monthly Notices of the Royal Astronomical Society. It challenges the conventional ideas on the role of dark matter in galaxy formation and the evolution of galaxies.

Universes are created on the supercomputer and then compared to real ones which help in identifying the rules. This research managed to create self-consistent universes for the first time which are replicas of the real one and simulations which contain 12 million galaxies spanning over 400 million years.

The universes were put through several tests to understand how galaxies appeared in the simulated universe compared to the real one. The universe resembling ours had similar physical rules.

The results from “UniverseMachine” have helped to resolve as to why galaxies stop making new stars even when plenty of hydrogen gas and other raw materials are present.

The classical theories suggest the presence of supermassive black holes in the galactic centres prevent gases to cool down to form stars. Similarly, dark matter heats up the surrounding gas and prevents forming stars. However, it was found that many galaxies in the universe were more likely to form stars at higher rates which is a contradiction. The team then created virtual galaxies in which the opposite happened. The universe based on current theories which stopped star formation early on appear much redder they actually are. The galaxy appears red due to its age and moving away faster, which shifts the light into the red spectrum called “redshift”. Also if a galaxy stops forming stars, there will be lesser blue stars and old red stars will be left.

If galaxies stopped creating stars, the colour of the universe would have been entirely different, hence it can be concluded that galaxies formed stars more efficiently in the earlier than we expected and the energy from the black holes and exploding stars is less efficient in decreasing the formation of stars.

A mock universe requires huge complexity which requires an entirely new approach not limited by computing power or memory and provided enough resolution to observe both supernovae as well as a major portion of the universe. Simulating a galaxy needs 10 to the 48th computing operations. The team used the “Ocelote” supercomputer at the UA High-Performance Computing cluster. 2000 processors churned the data for three weeks and over the course of the project, the team generated 8 million universes. The team took past 20 years of observations and compared them to the millions of mock universes generated and checked for matches. They plan to expand the UniverseMachine to include the morphology of galaxies and how their shapes evolve over time.

Journal Reference: Monthly Notices of the Royal Astronomical Society

big bang expansion

New research claims dark matter might be older than the Big Bang

Dark matter may be considered as the universe’s biggest mystery. It is known that something makes objects faster than they should but we do not actually know what it is and where it came from.

The origins of dark matter might be even more peculiar than it is known. They might be particles that appeared for a very brief amount of time before the Big Bang occurred. This not only suggests a new connection between astronomy and particle physics, but it could also indicate a new technique for searching mysterious stuff.

Tommi Tenkanen, a physicist at Johns Hopkins University said that if the dark matter comprises of new particles which were born before Big Bang then it affects the distribution of the galaxies in a unique manner. The connection may bring new conclusions about the time before Big Bang too. The paper by Tommi Tenkanen has been published in the journal Physical Review Letters.

The beginning of the Universe is a murky time period and the order of events is tangled up. It is still being debated about the events Big Bang comprised of. There is also cosmic inflation, a very small time period in which the Universe expanded like a balloon. It is accepted that it occurred in the range of 10-36 to 10-32 seconds after Big Bang took place. Some scientists feel that it occurred just before Big Bang took place. Avi Loeb, Hardvard-Smithsonian physicist said that cosmic inflation right now is a flexible idea which cannot be falsified experimentally.

Dark matter which comprises 80 percent of matter present in the Universe is considered Big Bang’s product sometimes. However, scientists feel if it were truly a product of Big Bang, there would have been evidences in experiments of particle physics. Instead, Tenkanen’s mathematical modelling suggests that it could have been a result of cosmic inflation. If cosmic inflation occurred before Big Bang then it implies that dark matter was present before everything in the Universe.

It also brings the idea that scalar particles could lead to dark matter. These particles have a spin of zero and according to inflaton theory, they were produced during cosmic inflation in a blink of the eye. The detection of Higgs boson, a scalar particle did not tell us much about dark matter.

Dark matter might be revealed in astronomical observations. We might know more about the origin of dark matter after the launch of the Euclid satellite in 2022. It might present some interesting revelations about Dark Matter and the time period before the Big Bang. Although the discussion right now is mainly theoretical, the search for dark matter will be fascinating in the coming times.

Journal: Physical Review Letters

abell 85

Researchers detect a gigantic black hole weighing 40 billion times more than Sun

Black holes can be very big, but there is a separate class which is huge and monstrous. Astronomers have identified such a giant black hole whose mass is 40 billion times that of the Sun. It is present at a galaxy’s centre that is known as Holmberg 15A. It is a supergiant elliptical galaxy present at a distance of 700 million light-years away from us that sits at the centre of the galaxy cluster, Abell 85.

 This new black hole is one of the largest black holes that have been identified and is the largest among the ones detected by tracking the motion of the stars around it. Past calculations based on the galaxy’s dynamics and its cluster found the mass of Holm 15A*(the black hole) which estimates it to be 310 billion times that of the Sun’s mass. These were indirect measurements of the black hole. The first direct measurement is obtained in this research and the paper has been submitted for peer review to The Astrophysical Journal.

Researchers mentioned in the paper that they used orbit-based, axisymmetric Schwarzschild models for analysing the stellar kinematics of Holm 15A from better resolution, spectral observations obtained with the help of MUSE at VLT. They found a supermassive black hole of mass (4.0 ± 0.80) × 1010 solar masses at Holm 15A’s center. This is the most massive black which has been detected directly in the local Universe.

The black hole with the greatest mass which has been detected so far is quasar TON 618, which weighs nearly 66 billion times the Sun’s mass according to indirect measurements. Event horizon of Holm 15A* which is also called as Schwarzschild radius would be enough to engulf the orbits of all the planets in Solar System and still have space left for some more. Pluto is 39.5 astronomical units from Sun. Heliopause is estimated to be nearly 123 AU. According to the mass of Holm 15A*, the Schwarzschild radius would be 790 AU.

The supermassive black hole of Holm 15A is almost four to nine times bigger than estimated according to stellar velocity and bulge stellar mass of the galaxy. It fits the collision model between two early-type galaxies that have depleted cores. It occurs when there are not many stars present in the core according to the number of stars which are there in the galaxy’s outer regions.

Researchers mentioned that the masses of black holes in cored galaxies such as Holm 15A vary inversely to the mass density and the central stellar surface brightness. They intend to keep studying about the black hole and conduct complex, detailed modelling thereby compare the results with the observations. This can help to understand how often such a merger occurs and how many such black holes remain yet to be discovered.

Journal Reference: arXiv

Ghosts of Ancient Explosions Live on in Stars Today

Ghosts of Ancient Explosions Live on in Stars Today

When small, dense stars called white dwarfs explode, they produce bright, short-lived flares called Type Ia supernovae. These supernovae are informative cosmological markers for astronomers—for example, they were used to prove that the universe is accelerating in its expansion.

White dwarfs are not all the same, ranging from half of the mass of our sun to almost 50 percent more massive than our sun. Some explode in Type Ia supernovae; others simply die quietly. Now, by studying the “fossils” of long-exploded white dwarfs, Caltech astronomers have found that early on in the universe, white dwarfs often exploded at lower masses than they do today. This discovery indicates that a white dwarf could explode from a variety of causes, and does not necessarily have to reach a critical mass before exploding.

A paper about the research, led by Evan Kirby, assistant professor of astronomy, appears in the Astrophysical Journal.

Near the end of their lives, a majority of stars like our sun dwindle down into dim, dense white dwarfs, with all their mass packed into a space about the size of Earth. Sometimes, white dwarfs explode in what’s called a Type Ia (pronounced one-A) supernova.

It is uncertain why some white dwarfs explode while others do not. In the early 1900s, an astrophysicist named Subrahmanyan Chandrasekhar calculated that if a white dwarf had more than 1.4 times the mass of our sun, it would explode in a Type Ia supernova. This mass was dubbed the Chandrasekhar mass. Though Chandrasekhar’s calculations gave one explanation for why some more massive white dwarfs explode, it did not explain why other white dwarfs less than 1.4 solar masses also explode.

Studying Type Ia supernovae is a time-sensitive process; they flare into existence and fade back into darkness all within a few months. To study long-gone supernovae and the white dwarfs that produced them, Kirby and his team use a technique colloquially called galactic archaeology.

Galactic archaeology is the process of looking for chemical signatures of long-past explosions in other stars. When a white dwarf explodes in a Type Ia supernova, it pollutes its galactic environment with elements forged in the explosion—heavy elements like nickel and iron. The more massive a star is when it explodes, the more heavy elements will be formed in the supernova. Then, those elements become incorporated into any newly forming stars in that region. Just as fossils today give clues about animals that have long ceased to exist, the amounts of nickel in stars illustrates how massive their long-exploded predecessors must have been.

Using the Keck II telescope, Kirby and his team first looked at certain ancient galaxies, those that ran out of material to form stars in the first billion years of the universe’s life. Most of the stars in these galaxies, the team found, had relatively low nickel content. This meant that the exploded white dwarfs that gave them that nickel must have been relatively low mass—about as massive as the sun, lower than the Chandrasekhar mass.

Yet, the researchers found that the nickel content was higher in more recently formed galaxies, meaning that as more time went by since the Big Bang, white dwarfs had begun to explode at higher masses.

“We found that, in the early universe, white dwarfs were exploding at lower masses than later in the universe’s lifetime,” says Kirby.”It’s still unclear what has driven this change.”

Understanding the processes that result in Type Ia supernovae is important because the explosions themselves are useful tools for making measurements of the universe. Regardless of how they exploded, most Type Ia supernovae follow a well-characterized relationship between their luminosity and the time it takes for them to fade.

“We call Type Ia supernovae ‘standardizable candles.’ If you look at a candle at a distance, it will look dimmer than when it’s up close. If you know how bright it is supposed to be up close, and you measure how bright it is at a distance, you can calculate that distance,” says Kirby. “Type Ia supernovae have been very useful in calculating things like the rate of expansion of the universe. We use them all the time in cosmology. So, it’s important to understand where they come from and characterize the white dwarfs that generate these explosions.”

The next steps are to study elements other than nickel, in particular, manganese. Manganese production is very sensitive to the mass of the supernova that produces it, and therefore gives a precise way to validate the conclusions drawn by the nickel content.

Materials provided by California Institute of Technology

Astrophysical shock phenomena reproduced in the laboratory

Astrophysical shock phenomena reproduced in the laboratory

Vast interstellar events where clouds of charged matter hurtle into each other and spew out high-energy particles have now been reproduced in the lab with high fidelity. The work, by MIT researchers and an international team of colleagues, should help resolve longstanding disputes over exactly what takes place in these gigantic shocks.

Many of the largest-scale events, such as the expanding bubble of matter hurtling outward from a supernova, involve a phenomenon called collisionless shock. In these interactions, the clouds of gas or plasma are so rarefied that most of the particles involved actually miss each other, but they nevertheless interact electromagnetically or in other ways to produces visible shock waves and filaments. These high-energy events have so far been difficult to reproduce under laboratory conditions that mirror those in an astrophysical setting, leading to disagreements among physicists as to the mechanisms at work in these astrophysical phenomena.

Now, the researchers have succeeded in reproducing critical conditions of these collisionless shocks in the laboratory, allowing for detailed study of the processes taking place within these giant cosmic smashups. The new findings are described in the journal Physical Review Letters, in a paper by MIT Plasma Science and Fusion Center Senior Research Scientist Chikang Li, five others at MIT, and 14 others around the world.

Virtually all visible matter in the universe is in the form of plasma, a kind of soup of subatomic particles where negatively charged electrons swim freely along with positively charged ions instead of being connected to each other in the form of atoms. The sun, the stars, and most clouds of interstellar material are made of plasma.

Most of these interstellar clouds are extremely tenuous, with such low density that true collisions between their constituent particles are rare even when one cloud slams into another at extreme velocities that can be much faster than 1,000 kilometers per second. Nevertheless, the result can be a spectacularly bright shock wave, sometimes showing a great deal of structural detail including long trailing filaments.

Astronomers have found that many changes take place at these shock boundaries, where physical parameters “jump,” Li says. But deciphering the mechanisms taking place in collisionless shocks has been difficult, since the combination of extremely high velocities and low densities has been hard to match on Earth.

While collisionless shocks had been predicted earlier, the first one that was directly identified, in the 1960s, was the bow shock formed by the solar wind, a tenuous stream of particles emanating from the sun, when it hits Earth’s magnetic field. Soon, many such shocks were recognized by astronomers in interstellar space. But in the decades since, “there has been a lot of simulations and theoretical modeling, but a lack of experiments” to understand how the processes work, Li says.

Li and his colleagues found a way to mimic the phenomena in the laboratory by generating a jet of low-density plasma using a set of six powerful laser beams, at the OMEGA laser facility at the University of Rochester, and aiming it at a thin-walled polyimide plastic bag filled with low-density hydrogen gas. The results reproduced many of the detailed instabilities observed in deep space, thus confirming that the conditions match closely enough to allow for detailed, close-up study of these elusive phenomena. A quantity called the mean free path of the plasma particles was measured as being much greater than the widths of the shock waves, Li says, thus meeting the formal definition of a collisionless shock.

At the boundary of the lab-generated collisionless shock, the density of the plasma spiked dramatically. The team was able to measure the detailed effects on both the upstream and downstream sides of the shock front, allowing them to begin to differentiate the mechanisms involved in the transfer of energy between the two clouds, something that physicists have spent years trying to figure out. The results are consistent with one set of predictions based on something called the Fermi mechanism, Li says, but further experiments will be needed to definitively rule out some other mechanisms that have been proposed.

“For the first time we were able to directly measure the structure” of important parts of the collisionless shock, Li says. “People have been pursuing this for several decades.”

The research also showed exactly how much energy is transferred to particles that pass through the shock boundary, which accelerates them to speeds that are a significant fraction of the speed of light, producing what are known as cosmic rays. A better understanding of this mechanism “was the goal of this experiment, and that’s what we measured” Li says, noting that they captured a full spectrum of the energies of the electrons accelerated by the shock.

“This report is the latest installment in a transformative series of experiments, annually reported since 2015, to emulate an actual astrophysical shock wave for comparison with space observations,” says Mark Koepke, a professor of physics at West Virginia University and chair of the Omega Laser Facility User Group, who was not involved in the study. “Computer simulations, space observations, and these experiments reinforce the physics interpretations that are advancing our understanding of the particle acceleration mechanisms in play in high-energy-density cosmic events such as gamma-ray-burst-induced outflows of relativistic plasma.”

Materials provided by Massachusetts Institute of Technology

A 3-D model of the Milky Way Galaxy using data from Cepheids

Astronomers generate the largest 3D model of Milky Way using Cepheid data

We do not possess a GPS system for our twisted and warped galaxy. As a result, astronomers have to be crafty for pointing our location among stars and producing maps of the Milky Way galaxy. Astronomers from the US and Europe successfully managed to create a 3D model of Milky Way galaxy which is based on the interstellar distance. The study has been published in the Science journal

It draws on the population of stars that are called Cepheids. They are massive, young, pulsing stars having brightness more than that of the Sun. The University of Warsaw ran a sky survey with the help of data from the Optical Gravitational Lensing Experiment from Las Campanas Observatory in Chile. Researchers managed to pick out 2,431 Cepheids through the thick dust and gas of Milky Way and used them for generating the map of the galaxy. 

Dorota Skowron, a researcher with Wroclaw University of Science and Technology and the study’s lead author said that the OGLE project observed the Milky Way’s galactic disk for a period of six years while capturing 206,726 sky images that contained 1,055,030,021 stars. In this they found the Cepheids population to be very useful for the purpose of map plotting since their brightness varies over time. 

This allowed the researchers to observe how bright the star actually is versus how it appears from the Earth. This difference between the two can inform us how far the star is from our Sun. With the help of this fluctuation, scientists produced the galaxy’s 3D model which confirmed the previous work that the galaxy is flared at the edges. They were able to determine the Cepheid’s age where the younger stars were closer to the center and older stars farther away from the galactic disk. 

With the simulation of star formation in the early Milky Way, scientists showed the evolution of the galaxy in past 175 million years with star formation in spiral arms resulting in distribution of Cepheids from 20 million to 260 million years old. Skowron hopes that the paper will be a good initial point for sophisticated modeling of our Galaxy’s past, as the Cepheids are a great testbed for checking the accuracy of the models. 

A study was earlier published in Nature Astronomy which looked at 1339 Cepheids and generated a comprehensive 3D map of Milky Way which found that our galaxy is twisted at the edges. It observed stars from the Wide-field Infrared Survey Explorer (WISE) of NASA. These two studies produced similar results which found about the warped edges of Milky Way. Both the studies relied on the fact that the Cepheids are present on our side of the Milky Way. An important question is whether there is a similar warp in the opposite side too.

Skowron does not think observing the other side will increase the probability of finding Cepheids. The future projects will observe the pulsing star found in our Galaxy called  RR Lyrae. They are present from an earlier time in the Milky Way and can provide another way of mapping the Galaxy. 

Journal Reference: Science journal

impression of pulsar planet

Astronomers discover a new type of strange pulsating star

Astronomers have discovered a type of very small, hot star which brightens and dims very often as the outer layers try to maintain an equilibrium. These stars are named as hot subdwarf pulsators and they might be related to a recently discovered rare star known as blue large-amplitude pulsator. The paper has been published in The Astrophysical Journal Letters.

Physicist Thomas Kupfer, Kavli Institute for Theoretical Physics, UC Santa Barbara said that there are many stars that pulsate including the Sun on a small scale. The ones having the largest brightness changes are known as radial pulsators which breath in and out as the size of the star changes. Although our Sun pulsates, its cycle is 11 years and the variation in brightness is only by 0.1 percent in the entire timeframe, hence it is not a pulsator in the truest sense. 

The brightness of the pulsators often vary by as much as 10 percent due to size and temperature change. 

Researchers identified four new stars from Zwicky Transient Facility survey that pulsate on timescales between 200 and 475 seconds with variation in brightness upto 5 percent. This change in brightness occurs in eclipsing binaries thus it was ruled out before being classified as a new type. Researchers then realised it to be subdwarf B stars

Subdwarf B stars are pretty small, about 10 percent of the sun’s size although very dense. In their small diameter, they pack in almost 20 to 50 percent of the mass of Sun. They are very bright as they burn at 20000 to 40000 Kelvin. It is considered that they form along a star’s evolutionary path upto eight times the mass of Sun when it dies.

As they run out of hydrogen to fuse in cores, they fuse helium turning to a red giant.  subdwarf B star is what happens when the outer hydrogen layers of a red giant are stripped away before helium fusion begins – possibly by a binary companion, but the exact mechanisms are unknown.

The V361 Hya class have a mode of pressure oscillation meaning that their pulsations are produced by the star’s internal pressure fluctuations. The V1093 Her class are gravity-mode pulsators that are produced by gravity waves. (not to be confused with gravitational waves).

Researchers are trying to find the exact mechanism of the oscillations of hot subdwarf pulsators although some believe it might be due to the unstable radial modes that are produced by iron kappa mechanism where iron buildup in star creates an energy layer resulting in pulsation. Subdwarf B stars are normally considered to be fusing helium, in their core or shell around the core. However, scientists believe that hot subdwarf pulsators lost the outer material before the helium was hot and dense.

Physicist Evan Bauer explained that rapid pulsations are understood by matching them to theoretical models where the low mass cores are composed of cold helium. The next step is to understand the actual mechanism behind pulsation and where the stars fit in the stellar evolution. 

Journal Reference:The Astrophysical Journal Letters