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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

black hole winds

Astronomers discover a super-fast star thrown out of the Milky Way

Many stars orbit near the Sagittarius A*, which is the super-massive black hole at the centre of the Milky Way galaxy. Some stars have been ripped apart when they got too close to the super-massive black hole. Other stars have changed colour due to the extremely high gravitational effects and in a few cases, the stars just slingshot into the intergalactic space like the S5-HVS1 star.

As reported in a paper available on the pre-print server arXiv, yet to be peer-reviewed, an international group of scientists have spotted a hypervelocity star as they were studying interesting objects for the Southern Stellar Stream Spectroscopic Survey(S5). The speed of hyper-velocity refers to a staggering 1,107 kilometres per second which is equivalent to 2.275 million miles per hour and could cover the distance between New York and Sydney in just 15.7 seconds.

There must be something that has accelerated to move the star at such high speed and a team of researchers are trying to estimate from where the star could most possibly come from. The most likely explanation based on their analysis is the core of the milky way which easily refers to the Sagittarius A*.

If the super-massive black hole is the real reason, then the star was probably kicked away with a velocity of more than 1800 kilometres per second and has been slowing down on its travel for about 4.8 million years. The star is a standard hydrogen fusing star or the main sequence object and is located close to 30,000 light-years from the Earth.

It is the fastest main sequence star which was ever discovered and it is not unique as astronomers have discovered dozens of stars like these and although many of such stars appear to have accelerated out of the galaxy by events other than the interactions with Sagittarius A*. Researchers are suggesting that if one of the two stars in a binary system goes supernova, it could be enough to push its companion beyond the disk of the Milky Way.

However, the stars are not only being kicked out as scientists have detected stars entering the galaxy from the smaller companions of Milky Way. They could have been also accelerated by a supernova or a supermassive black hole yet to be observed.

Journal Reference: arXiv


TESS satellite uncovers its ‘first nearby super-Earth’

TESS satellite uncovers its ‘first nearby super-Earth’

An international team of astronomers led by Cornell’s Lisa Kaltenegger has characterized the first potentially habitable world outside of our own solar system.

Located about 31 light-years away, the super-Earth planet – named GJ 357 d – was discovered in early 2019 owing to NASA’s Transiting Exoplanet Survey Satellite (TESS), a mission designed to comb the heavens for exoplanets, according to their new modeling research in the Astrophysical Journal Letters.

“This is exciting, as this is TESS’s first discovery of a nearby super-Earth that could harbor life – TESS is a small, mighty mission with a huge reach,” said Kaltenegger, associate professor of astronomy, director of Cornell’s Carl Sagan Institute and a member of the TESS science team.

The exoplanet is more massive than our own blue planet, and Kaltenegger said the discovery will provide insight into Earth’s heavyweight planetary cousins. “With a thick atmosphere, the planet GJ 357 d could maintain liquid water on its surface like Earth, and we could pick out signs of life with telescopes that will soon be online,” she said.

Astronomers from the Institute of Astrophysics of the Canary Islands and the University of La Laguna, both in Spain, announced the discovery of the GJ 357 system July 31 in the journal Astronomy & Astrophysics. They showed that the distant solar system – with a diminutive M-type dwarf sun, about one-third the size of our own sun – harbors three planets, with one of those in that system’s habitable zone: GJ 357 d.

Last February, the TESS satellite observed that the dwarf sun GJ 357 dimmed very slightly every 3.9 days, evidence of a transiting planet moving across the star’s face. That planet was GJ 357 b, a so-called “hot Earth” about 22% larger than Earth, according to the NASA Goddard Space Flight Center, which guides TESS.

Follow-up observations from the ground led to the discovery of two more exoplanetary siblings: GJ 357 c and GJ 357 d. The international team of scientists collected Earth-based telescopic data going back two decades – to reveal the newly found exoplanets’ tiny gravitational tugs on its host star, according to NASA.

Exoplanet GJ 357 c sizzles at 260 degrees Fahrenheit and has at least 3.4 times Earth’s mass. However, the system’s outermost known sibling planet – GJ 357 d, a super-Earth – could provide Earth-like conditions and orbits the dwarf star every 55.7 days at a distance about one-fifth of Earth’s distance from the sun. It is not yet known if this planet transits its sun.

Kaltenegger, doctoral candidate Jack Madden and undergraduate student Zifan Lin ’20 simulated light fingerprints, climates and remotely detectable spectra for a planet that could range from a rocky composition to a water world.

Madden explained that investigating new discoveries provides an opportunity to test theories and models. “We built the first models of what this new world could be like,” he said. “Just knowing that liquid water can exist on the surface of this planet motivates scientists to find ways of detecting signs of life.”

Lin described the work from an undergraduate perspective: “Working on a newly discovered planet is something of a dream come true. I was among the first group of people to model its spectra, and thinking about this still overwhelms me.”

In a nod to her institute’s namesake, the late Cornell professor Carl Sagan, Kaltenegger said: “If GJ 357 d were to show signs of life, it would be at the top of everyone’s travel list – and we could answer a 1,000-year-old question on whether we are alone in the cosmos.”

In addition to Kaltenegger, Madden and Lin, co-authors of “The Habitability of GJ 357d: Possible Climates and Observability,” include Sarah Rugheimer, Oxford University; Antigona Segura, National Autonomous University of Mexico (UNAM); Rafael Luque and Eric Pallé, both of the Institute of Astrophysics of the Canary Islands and the University of La Laguna; and Néstor Espinoza, Max Planck Institute for Astronomy, Germany.

Tour the GJ 357 system, located 31 light-years away in the constellation Hydra. Astronomers confirming a planet candidate identified by NASA’s Transiting Exoplanet Survey Satellite subsequently found two additional worlds orbiting the star.

Journal Reference: Astronomy & Astrophysics

Materials provided by Cornell University

Mini Sun

Researchers recreate mini sun for studying solar winds and plasma burps

The stars in our universe have a magnetic field that interacts with the winds which they produce including our sun. As a result of the collaboration between the Sun’s magnetic field and the solar wind leads to the formation of a heliospheric magnetic field like a spiralling structure known as the Parker spiral. This spiral is important for administering the plasma processes that source the solar wind.

According to a new study at the University of Wisconsin-Madison, the physicists have reported the creation of a mini sun like a laboratory model of the Parker spiral system based on the idea of rotating plasma magnetosphere and measurement of the global structure and dynamic behaviour. The study has been published in Nature Physics.

Physicists have access to this Big Red Ball, which is a three-meter wide hollow sphere which contains different probes and a strong magnet at the centre. The helium gas is siphoned and ionized to create plasma and then an applied electric field alongside the magnetic field which copies the ideal case of spinning plasma and the electromagnetic fields of the sun. Estimations can be taken at numerous points inside the bass which enables physicists to study the solar phenomena in three dimensions.

They have an option to replicate the Parker Spiral, a magnetic field which covers the entire solar system, the magnetic field transmits straight out of the sun. From there onwards, the solar wind dynamics take over and haul the magnetic field into a spiral.

A graduate student in the Physics department at UW-Madison, Ethan Peterson said that the satellite measurements are pretty consistent with the Parker Spiral model, only at one point at a time and so can never make simultaneous and map it on a large scale map. The plasma from the sun’s plasma burps fuel up the slow solar winds.

The speed of light and magnetic field are probed and the data has mapped a region where plasma is moving fast enough and where the plasma could break off and eject radially. The ejections have been spotted by satellites and no one knows the reason as to what drives them. They found similar burps in the experiment and found out how they developed.

The work has shown that understanding fundamental physics of these processes is possible through laboratory experiments and the Big Red Ball being funded as a National User Facility allows scientists to study the physics of solar winds. The Earthbound experiments can not replace satellite missions like the Parker Solar Probe which was launched in August 2018 can reach the Alfven surface and can even dip below it. It is expected to provide direct measurements of the solar wind.

Journal Reference: Nature Physics

black hole eating star

Researchers solve the mystery of small galaxies with supermassive black holes

Nearly every galaxy in the universe appears to have a black hole in the centre including our Milky Way galaxy. There is a strange relationship between the mass of black hole at the galactic centre and properties of the galactic host itself. So a bigger galaxy refers to a bigger black hole. However, some exceptions have been found to this trend and researchers have detected an important link between the evolution of galaxies and black holes.

We do not know which came first, the black hole or the galaxy. About thirteen and a half billion years ago galaxies and black holes formed nearly at the same time. According to astronomers, regular communication takes place between galaxies and their black holes. Bigger galaxies have more matter to feed their giant black holes. On feeding, the black holes become active. Gases swirl around it with high energies before falling onto the event horizon. Some part of the gas heats and radiation is emitted which escapes the vicinity. Gases can also swirl around the outer edges without falling in which form of long jets extending thousands of light-years in the nearby medium.

So, this energy which is dumped in the surrounding heats up the nearby gases and the heated gas has low inclination to sink into the centre where it might encounter the black hole. Thus the gas stays away and the black hole stabilizes in size as it cannot feed on anything. If a galaxy grows larger, then it can press more gas to the centre feeding the black hole followed by a feedback episode which holds the continued growth of black hole from getting out of control.

Thus smaller galaxies end up with smaller black holes and the larger ones with big black holes. However, there are exceptions to it, as some galaxies host the black holes way out of their ability to feed them. The reason could be due to a peculiar type of galaxy known as a blue nugget. These galaxies are found very far away meaning they were part of a younger universe. They are blue and small as their name suggests. They have an enhanced rate of star formation. Due to this, they form bigger and brighter stars than average. They are able to form stars at an exceptional rate since they feed on the nearby gas streams pumping material to the undersized galaxy.

However, this influx of raw material has its impacts and due to these activities, a massive black hole formation takes place at the centre. It feeds all over the galaxy shutting the further formation of stars. Due to their size, this event affects the entire galaxy terminating the growth at an early stage. So the stars which were formed eventually die as old, dim, red stars turning the galaxy into a red nugget. Thus it has an exceptionally large black hole at the centre. There are only handful of examples of such cases which can give insights into the relationship between galaxies and their black holes.

Journal Reference: arxiv

TESS discovers three new planets nearby, including temperate “sub-Neptune”

TESS discovers three new planets nearby, including temperate “sub-Neptune”

NASA’s Transiting Exoplanet Survey Satellite, or TESS, has discovered three new worlds that are among the smallest, nearest exoplanets known to date. The planets orbit a star just 73 light-years away and include a small, rocky super-Earth and two sub-Neptunes — planets about half the size of our own icy giant.

The sub-Neptune furthest out from the star appears to be within a “temperate” zone, meaning that the very top of the planet’s atmosphere is within a temperature range that could support some forms of life. However, scientists say the planet’s atmosphere is likely a thick, ultradense heat trap that renders the planet’s surface too hot to host water or life.

Nevertheless, this new planetary system, which astronomers have dubbed TOI-270, is proving to have other curious qualities. For instance, all three planets appear to be relatively close in size. In contrast, our own solar system is populated with planetary extremes, from the small, rocky worlds of Mercury, Venus, Earth, and Mars, to the much more massive Jupiter and Saturn, and the more remote ice giants of Neptune and Uranus.

There’s nothing in our solar system that resembles an intermediate planet, with a size and composition somewhere in the middle of Earth and Neptune. But TOI-270 appears to host two such planets: both sub-Neptunes are smaller than our own Neptune and not much larger than the rocky planet in the system.

Astronomers believe TOI-270’s sub-Neptunes may be a “missing link” in planetary formation, as they are of an intermediate size and could help researchers determine whether small, rocky planets like Earth and more massive, icy worlds like Neptune follow the same formation path or evolve separately.

TOI-270 is an ideal system for answering such questions, because the star itself is nearby and therefore bright, and also unusually quiet. The star is an M-dwarf, a type of star that is normally extremely active, with frequent flares and solar storms. TOI-270 appears to be an older M-dwarf that has since quieted down, giving off a steady brightness, against which scientists can measure many properties of the orbiting planets, such as their mass and atmospheric composition.

“There are a lot of little pieces of the puzzle that we can solve with this system,” says Maximilian Günther, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research and lead author of a study published today in Nature Astronomy that details the discovery. “You can really do all the things you want to do in exoplanet science, with this system.”

Compare and contrast worlds in the TOI 270 system with these illustrations. Temperatures given for TOI 270 planets are equilibrium temperatures, calculated without the warming effects of any possible atmospheres. Credit: NASA’s Goddard Space Flight Center

A planetary pattern

Günther and his colleagues detected the three new planets after looking through measurements of stellar brightness taken by TESS. The MIT-developed satellite stares at patches of the sky for 27 days at a time, monitoring thousands of stars for possible transits — characteristic dips in brightness that could signal a planet temporarily blocking the star’s light as it passes in front of it.

The team isolated several such signals from a nearby  star, located 73 light years away in the southern sky. They named the star TOI-270, for the 270th “TESS Object of Interest” identified to date. The researchers used ground-based instruments to follow up on the star’s activity, and confirmed that the signals are the result of three orbiting exoplanets: planet b, a rocky super-Earth with a roughly three-day orbit; planet c, a sub-Neptune with a five-day orbit; and planet d, another sub-Neptune slightly further out, with an 11-day orbit.

Günther notes that the planets seem to line up in what astronomers refer to as a “resonant chain,” meaning that the ratio of their orbits are close to whole integers — in this case, 3:5 for the inner pair, and 2:1 for the outer pair — and that the planets are therefore in “resonance” with each other. Astronomers have discovered other small stars with similarly resonant planetary formations. And in our own solar system, the moons of Jupiter also happen to line up in resonance with each other.

“For TOI-270, these planets line up like pearls on a string,” Günther says. “That’s a very interesting thing, because it lets us study their dynamical behavior. And you can almost expect, if there are more planets, the next one would be somewhere further out, at another integer ratio.”

“An exceptional laboratory”

TOI-270’s discovery initially caused a stir of excitement within the TESS science team, as it seemed, in the first analysis, that planet d might lie in the star’s habitable zone, a region that would be cool enough for the planet’s surface to support water, and possibly life. But the researchers soon realized that the planet’s atmosphere was probably extremely thick, and would therefore generate an intense greenhouse effect, causing the planet’s surface to be too hot to be habitable.

But Günther says there is a good possibility that the system hosts other planets, further out from planet d, that might well lie within the habitable zone. Planet d, with an 11-day orbit, is about 10 million kilometers out from the star. Günther says that, given that the star is small and relatively cool — about half as hot as the sun — its habitable zone could potentially begin at around 15 million kilometers. But whether a planet exists within this zone, and whether it is habitable, depends on a host of other parameters, such as its size, mass, and atmospheric conditions.

Fortunately, the team writes in their paper that “the host star, TOI-270, is remarkably well-suited for future habitability searches, as it is particularly quiet.” The researchers plan to focus other instruments, including the upcoming James Webb Space Telescope, on TOI-270, to pin down various properties of the three planets, as well as search for additional planets in the star’s habitable zone.

“TOI-270 is a true Disneyland for exoplanet science, and one of the prime systems TESS was set out to discover,” Günther says. “It is an exceptional laboratory for not one, but many reasons — it really ticks all the boxes.”

Materials provided by Massachusetts Institute of Technology

The Solar Cycle XRay

Researchers have solved one of the biggest mysteries behind sunspot cycles

Waxing and waning of sunspots is a part of the natural cycle of Sun. However, astronauts do not yet understand this phenomenon fully. Now, new research has brought the conclusion that particular “terminator” events are responsible for ending the sunspot cycles which means that they can be predicted in a better way. Predicting sunspot cycles would mean that advanced warning of the various types of solar storms that could change infrastructure and electronics on Earth. The study has been published in the Solar Physics and Scientific Reports

These findings are based on 140 years of solar observations. They include recordings of coronal bright points which occur during relatively calm periods on the Sun. Researchers say that movement and final disappearance of these points mark a terminator event. Scott McIntosh, an astrophysicist from National Center for Atmospheric Research, US said that this evidence was hidden in the observations for more than a century however we were not aware of what we were finding. Combination of such a wide scale of observations gives new insights to how the interior of the Sun drives solar cycle. 

A sunspot cycle lasts nearly 11 years. After a solar minimum, sunspots slowly increase in number, forming at a latitude of 35 degrees in both hemispheres before reaching the equator and then dying. This takes nearly a decade to complete, with the midpoint being called the solar maximum when the sunspot activity is highest. Recent solar maximum was in April 2014.

The coronal bright points also travel towards the equator from higher latitudes. They overlap with sunspots at some points and scientists think them to be the markers for toroidal magnetic field movement. These wrap around the Sun also moving towards equator. When magnetic fields rise to Sun’s surface, scientists propose that sunspots emerge for joining the coronal bright points. Plasma is built as the spots move and is released when one wave of toroidal magnetic field hits the another in the opposite direction on the equator. 

This release is often quite dramatic. Research tells that solar tsunami of plasma is unleashed, which travels further away from the equator at 300 metres per second. This again meets another toroidal magnetic field in the opposite direction, leading to the formation of sunspots and the cycle continues. 

Although this is a hypothesis presently with the accumulated data and educated guesswork and scientists will be testing their models when the current solar cycle ends and start again the next year. This research shows that observations and multiple data streams can unlock the discoveries which would be more difficult otherwise. Bob Leamon from University of Maryland says that the terminators were identified by observing different types of solar activity, magnetic fields, spectral irradiance, radio flux along with bright points. This shows that along with spacecrafts, we need to use all the data available to understand how things work. 

Journal Reference: Scientific Reports