stellar physics



** Synopsis: A blast of gamma rays from space detected in June 2016 is helping astronomers resolve long-standing questions about the universe’s most powerful explosions. **

In June 2016, an international team of 31 astronomers, led by the University of Maryland’s Eleanora Troja and including Arizona State University’s Nathaniel Butler, caught a massive star as it died in a titanic explosion deep in space.

The blast of the dying star released in about 40 seconds as much energy as the Sun releases over its entire lifetime, all focused into a tight beam of gamma rays aimed by chance toward Earth.

The team’s findings, reported in the scientific journal Nature, provide strong evidence for one of two competing models for how gamma-ray bursters (GRBs) produce their energy.

“These are the brightest explosions in the universe,” says Butler, an associate professor in ASU’s School of Earth and Space Exploration. “And we were able to measure this one’s development and decay almost from the initial blast.”

Quick reflexes

The gamma-ray blast on June 25, 2016, was detected by two NASA satellites that monitor the sky for such events, the Fermi Gamma-ray Space Telescope and the Swift Gamma-Ray Burst Mission.

The satellite observatories detected the burst of gamma rays, identified where in the sky it came from, and sent its celestial position within seconds to automated telescopes on the ground.

The MASTER-IRC telescope at the Teide Observatory in the Canary Islands observed it first, within a minute of the satellite notification. The telescope is part of Russia’s MASTER network of robotic telescopes at the Teide Observatory. It made optical light observations while the initial phase was still active, gathering data on the amount of polarized optical light relative to the total light produced.

After the Sun set over this facility eight and a half hours later, the RATIR camera in which ASU is involved began observing. RATIR stands for Reionization And Transients InfraRed camera; it is mounted on a 1.5-meter (60-inch) robotically controlled telescope located on San Pedro Mártir Peak, at Mexico’s National Astronomical Observatory in Baja California. Butler is the principal investigator for the fully-automated camera.

Butler explains, “At best, it takes a minute or two for our telescope to slew to the burst’s position. In this case, we had to wait for it to rise over the horizon. This means the gamma-ray burst itself had ended, and we were observing what’s called the afterglow. This is the fading explosion as the radiation shocks up the interstellar medium around the star that exploded.”

He says, “The RATIR camera lets us take simultaneous images in six colors, two optical and four near-infrared. Over the past five years, RATIR has imaged 155 gamma-ray bursts.”

Mystery beams of energy

While gamma-ray bursters have been known for about fifty years, astronomers are still mostly in the dark about how they erupt.

“Despite a long history of observations,” Butler says, “the emission mechanism driving gamma-ray bursters remains largely mysterious.”

Gamma-ray bursts are detected approximately once per day and are brief, but intense, flashes of gamma radiation. They come from all different directions in the sky, and they last from tens of milliseconds to about a minute, making it hard to observe them in detail.

Astronomers believe most of these explosions are associated with supernovas. These occur when a massive star reaches the end of its normal existence and blows up in a colossal explosion. A supernova throws off some of the star’s outer layers, while its core and remaining layers collapse in a few seconds into a neutron star or, in the case of highly massive stars, a black hole.

Continued RATIR observations over weeks following the June 2016 outburst showed that the gamma rays were shot out in a beam about two degrees wide, or roughly four times the apparent size of the Moon. It was sheer chance that Earth happened to lie within the beam.

Beaming effects, Butler says, may result from the spin of the black hole produced after the supernova explosion, as it releases material along its poles.

Magnetic focus

“We think the gamma-ray emission is due to highly energetic electrons, propelled outward like a fireball,” Butler says. Magnetic fields must also be present, he adds, and theories differ as to how the fields are produced and to what extent the flow of magnetic energy outward is important.

A key diagnostic is measuring the radiation’s polarization, he explains. This, astronomers think, is largely controlled by the strength of the magnetic fields that focus the radiation. Butler says, "Measuring the strength of magnetic fields by their polarization effects can tell us about the mechanisms that accelerate particles such as electrons up to very high energies and cause them to radiate at gamma-ray energies.”

In the case of the June 2016 blast, the scientists were able to measure polarization using MASTER within minutes, an unprecedented early discovery. The large amount of polarization the team observed indicates that powerful magnetic fields were confining and directing it. This lends support for the magnetic origin model for gamma-ray bursters.

While gamma-ray bursters have many more mysteries to be unfolded, Butler says, “this is the first strong evidence that the early shocks generated by these bursts are magnetically driven.”

I paid the small domes of the Tartu Observatory (Estonia) a visit after discussing my bachelor thesis with supervisors ❄
I’m currently reducting spectral data of a yellow hypergiant V509 Cassiopeiae, one of the most rare type of stars in the Universe. Its evolution is so rapid—in 20 years, V509 Cas ejected a solar mass of material—that its spectrum is changing, and I’ll inspect a forbidden NII emission line to find out about the star’s brightness. More about this once when I’m at the writing part!


Kepler satellite discovers variability in the Seven Sisters

The Seven Sisters, as they were known to the ancient Greeks, are now known to modern astronomers as the Pleiades star cluster - a set of stars which are visible to the naked eye and have been studied for thousands of years by cultures all over the world.

Now Dr Tim White of the Stellar Astrophysics Centre at Aarhus University and his team of Danish and international astronomers have demonstrated a powerful new technique for observing stars such as these, which are ordinarily far too bright to look at with high performance telescopes. Their work is published in the Monthly Notices of the Royal Astronomical Society.

Using a new algorithm to enhance observations from the Kepler Space Telescope in its K2 Mission, the team has performed the most detailed study yet of the variability of these stars.

Satellites such as Kepler are engineered to search for planets orbiting distant stars by looking for the dip in brightness as the planets pass in front, and also to do asteroseismology, studying the structure and evolution of stars as revealed by changes in their brightness.

Because the Kepler mission was designed to look at thousands of faint stars at a time, some of the brightest stars are actually too bright to observe.

Aiming a beam of light from a bright star at a point on a camera detector will cause the central pixels of the star’s image to be saturated, which causes a very significant loss of precision in the measurement of the total brightness of the star. This is the same process which causes a loss of dynamic range on ordinary digital cameras, which cannot see faint and bright detail in the same exposure.
“The solution to observing bright stars with Kepler turned out to be rather simple,” said lead author Dr Tim White. “We’re chiefly concerned about relative, rather than absolute, changes in brightness. We can just measure these changes from nearby unsaturated pixels, and ignore the saturated areas altogether.”

But changes in the satellite’s motion and slight imperfections in the detector can still hide the signal of stellar variability. To overcome this, the authors developed a new technique to weight the contribution of each pixel to find the right balance where instrumental effects are cancelled out, revealing the true stellar variability. This new method has been named halo photometry, a simple and fast algorithm the authors have released as free open-source software.

Most of the seven stars are revealed to be slowly-pulsating B stars, a class of variable star in which the star’s brightness changes with day-long periods. The frequencies of these pulsations are key to exploring some of the poorly understood processes in the core of these stars.

The seventh star, Maia, is different: it varies with a regular period of 10 days. Previous studies have shown that Maia belongs to a class of stars with abnormal surface concentrations of some chemical elements such as manganese. To see if these things were related, a series of spectroscopic observations were taken with the Hertzsprung SONG Telescope.

“What we saw was that the brightness changes seen by Kepler go hand-in-hand with changes in the strength of manganese absorption in Maia’s atmosphere,” said Dr Victoria Antoci, a co-author of the work and Assistant Professor at the Stellar Astrophysics Centre, Aarhus University. “We conclude that the variations are caused by a large chemical spot on the surface of the star, which comes in and out of view as the star rotates with a ten day period.”

“Sixty years ago, astronomers had thought they could see variability in Maia with periods of a few hours and suggested this was the first of a whole new class of variable stars they called ‘Maia Variables’,” White said, “but our new observations show that Maia is not itself a Maia Variable!”

No signs of exoplanetary transits were detected in this study, but the authors show that their new algorithm can attain the precision that will be needed for Kepler and future space telescopes such as the Transiting Exoplanet Survey Satellite (TESS) to detect planets transiting stars as bright as our neighbouring star Alpha Centauri.

These nearby bright stars are the best targets for future missions and facilities such as the James Webb Space Telescope, which is due to launch in late 2018.

TOP IMAGE….This image from NASA’s Kepler spacecraft shows members of the Pleiades star cluster taken during Campaign 4 of the K2 Mission. The cluster stretches across two of the 42 charge-coupled devices (CCDs) that make up Kepler’s 95 megapixel camera. The brightest stars in the cluster – Alcyone, Atlas, Electra, Maia, Merope, Taygeta, and Pleione – are visible to the naked eye. Kepler was not designed to look at stars this bright; they cause the camera to saturate, leading to long spikes and other artifacts in the image. Despite this serious image degradation, the new technique has allowed astronomers to carefully measure changes in brightness of these stars as the Kepler telescope observed them for almost three months. Credit: NASA / Aarhus University / T. White

LOWER IMAGE….The unique brightness fluctuations of each star reveal clues about their physical properties such as their size and rotation rate. Most of the bright stars in the Pleiades are a type of variable star called a slowly pulsating B star, but Maia is different, and shows evidence of a large chemical spot that crosses its surface as the star rotates with a 10-day period. Credit: Aarhus University / T. White

miscellaninousgarbage  asked:

What's a neutron star? I read about them in Bill Bryson's book, but I couldn't figure out why a neutron start would happen in the first place?

When massive stars collapse, the core of the star gets compressed extremely tightly by the force of its own gravity. As the core collapses, the electrons and protons in the core get closer and closer together. Eventually, the core gets so dense that the electrons and protons are forced together, combining into neutrons. The entire core becomes essentially a solid ball of neutrons, as dense as an atomic nuclei. The outer layers of the star, which are also rushing in towards the core, bounce off of this rock-hard layer of neutrons and whiz off into space, creating a supernova and leaving behind a neutron star at the center. And all of this happens in less than a second. Pretty wild. To summarize: neutron stars are giant balls of neutrons that resulted when a stellar core collapsed and became so dense the protons and electrons combined into neutrons. 

Side note: Robert L. Forward wrote a really interesting novel called Dragon’s Egg, which was about intelligent life on a neutron star! It’s quite an interesting read, and you learn a whole lot about neutron stars since the author has a Ph.D in physics. If you want a copy, you can find it here; you won’t find it at a bookstore because it’s out of print, but you can find a used copy online (I linked to one). Let me know if you have any other questions, I’m happy to answer them!

Bachelor of Science in Physics: ✔

This marks the end of my studies in University of Tartu. My thesis was about stellar physics, but over time, I have become more interested in the Solar System bodies and I wish to research Mars from here on. There are exciting times ahead for space exploration as our technical capabilities are only advancing, and I can’t wait to be part of this field ✨    

Shout-out to my lovely friend, who modified my Pink Floyd t-shirt for graduation 😄

Cool Facts about the Sun

1. The Sun weighs about one solar mass. You could fit approximately 1 Sun inside it.

2. Light takes thousands of years to travel from the core of the Sun to the surface. This is because solar law requires exiting photons to form a queue.

3. The Sun is most luminous in the sleep ray part of the electromagnetic spectrum. Scientists plan to send out probes made of cat bellies to image these rays without interference from the atmosphere.

4. The Sun got a B average in star school, so it’s brighter than ~85% of stars.

5. Whenever the ancient Aztecs would offer up the beating hearts of human sacrifices to their sun god, the Sun would have lots of failed solar eruptions. Basically it kind of puked in disgust but the plasma fell back onto its face.

6. The Sun’s LinkedIn profile says its career is “proton marriage counselor.”

7. Sunspots are the Sun giving itself skin cancer.

8. The Sun sometimes sends out special messages in its neutrinos, but nobody ever detects enough to find them. 

9. Mercury moves the fastest of all the planets because the Sun is constantly trying to murder it.

10. If you were to take the Sun and crush it to the size of Manhattan, you’d be the strongest person alive. 

The signs as sciences

Aries:  Aeronautics// Aircraft design, construction, and navigation.

Taurus:  Astrophysics // The branch of astronomy that deals with the physics of stellar phenomena.

Gemini:  Gelotology // The study of laughter.

Cancer:  Cosmology // The study of the physical universe considered as a totality of phenomena in time and space.

Leo:  Robotics // The science of technology to design, fabrication, and application of robots.

Virgo:  Astronomy // The study of outer space.

Libra:  Oceanography // The exploration and study of the ocean.

Scorpio:  Horology // The science of measuring time and making time pieces

Sagittarius:  Cartography // The art or technique of making maps or charts.

Capricorn:  Volcanology // The study of volcanoes and volcanic phenomena.

Aquarius:  Meteorology // The study of weather and atmospheric conditions including whether phenomenas 

Pisces:  Botany // The study of plants.

Earth-like atmosphere may not survive Proxima b's orbit

Proxima b, an Earth-size planet right outside our solar system in the habitable zone of its star, may not be able to keep a grip on its atmosphere, leaving the surface exposed to harmful stellar radiation and reducing its potential for habitability.

At only four light-years away, Proxima b is our closest known extra-solar neighbor. However, due to the fact that it hasn’t been seen crossing in front of its host star, the exoplanet eludes the usual method for learning about its atmosphere. Instead, scientists must rely on models to understand whether the exoplanet is habitable.

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Celestial Wonders- Binary Stars.

The twins of the stellar world are binary star systems.A binary star is a star system consisting of two stars orbiting around their common center of mass.When two stars appear close together in the sky, the situation is known as an “optical double”. This means that although the stars are aligned along the same line of sight, they may be at completely different distances from us. This occurs in constellations; however, two stars in the same constellation can also be part of a binary system.

Artist’s impression of the sight from a (hypothetical) moon of planet HD 188753 Ab (upper left), which orbits a triple star system( yes, a Triple Star system!). The brightest companion is just below the horizon.

Binary star systems are very important in astrophysics because calculations of their orbits allow the masses of their component stars to be directly determined, which in turn allows other stellar parameters, such as radius and density, to be indirectly estimated. This also determines an empirical mass-luminosity relationship (MLR) from which the masses of single stars can be estimated.

It is estimated that approximately 1/3 of the star systems in the Milky Way are binary or multiple, with the remaining 2/3 consisting of single stars.

The Brightest star in the sky is a binary.

This is true. When it was discovered in 1844 by the German astronomer Bessel, the system was classed as an astrometric binary, because the companion star, Sirius B, was too faint to be seen. Bessel, who was also a mathematician, determined by calculations that Sirius B existed after observing that the proper of Sirius A (the main star) followed a wavy path in the sky, rather than a uniform path. Sirius can now be studied as a visual binary because, with improving technology and therefore improved telescopes, Sirius B was able to be seen, although not for 20 years after Bessel had correctly predicted its existence.

Black Holes in a binary System ?

The term “binary system” is not used exclusively for star systems, but also for planets, asteroids, and galaxies which rotate around a common center of gravity. However, this is not a trick question; even in star binaries, the companion can be a black hole. An example of this is Cygnus X-1.

The universe is pretty amazing huh?…

komradekrispy  asked:

Can you kill a star?

yes, like any fusion reaction a star can theoretically be stopped before reaching exhaustion of the limiting reactant by a massive force or anti matter. Stars are basically plasma and gas, not really a giant fire, adding more mass to them only increases the reserves of what element they are crushing together to form another element, (hydrogen being fused to create helium in the case of our sun currently) you would need some way to siphon and use up all the helium produced so the sun would have no way to switch over to helium fusion when it runs out of hydrogen, but we are still talking billions of years here. you would need to somehow remove the very core of the sun, which would be very hard to do. 

You would need some way to manipulate gravity to siphon the core of the sun out, to eject the suns core and basically suck it up, like a blackhole of some kind, then again, its gonna do a lot more than just that star, you would take out that entire solar system and start sucking in nearby stars.  it would be akin to dropping an atomic bomb to kill a single ant.

Antimatter would be the way to go, the reaction and annihilation event that would occur would be catastrophic, you would need so much antimatter, and theres nothing quite as dangerous and unwise as a weapon that requires constant suspension inside a perfect vacuum using gravitational forces at all times, or else you risk blowing up your entire planet. how one would contain and produce antimatter on that level is unknown, we don’t know that much about it, we know far more about the theory of evolution than we know about the theory of gravity.  you get into some quantum physics and advanced stuff that is way beyond my scope at that point. 

really, its a lot easier to ruin all the planets around a star than it is to destroy a star itself. 

anonymous asked:

8 - kara/lena for the kiss meme please 😄

8 - kiss in the dark

As a child, Lena was obsessed with the stars. It was not the physics of stellar geometry that fascinated Lena, but the twinkle, like a thousand teary eyes all crying out in unison. They’re a scar on her memory now, of lying in a pool of fast growing blood while her parents struggled to save her, onto to eat a pair of bullets to the back of the skull themselves. Stars were the last thing Lena saw, winking steadily out of existence as her consciousness faded, when her parents died.

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Researchers propose how the universe became filled with light

Black holes may have punctured darkened galaxies, allowing light to escape

Soon after the Big Bang, the universe went completely dark.

The intense, seminal event that created the cosmos churned up so much hot, thick gas that light was completely trapped. Much later–perhaps as many as one billion years after the Big Bang–the universe expanded, became more transparent, and eventually filled up with galaxies, planets, stars, and other objects that give off visible light. That’s the universe we know today.

How it emerged from the cosmic dark ages to a clearer, light-filled state remains a mystery.

In a new study, researchers at the University of Iowa offer a theory of how that happened. They think black holes that dwell in the center of galaxies fling out matter so violently that the ejected material pierces its cloudy surroundings, allowing light to escape. The researchers arrived at their theory after observing a nearby galaxy from which ultraviolet light is escaping.

“The observations show the presence of very bright X-ray sources that are likely accreting black holes,” says Philip Kaaret, professor in the UI Department of Physics and Astronomy and corresponding author on the study. “It’s possible the black hole is creating winds that help the ionizing radiation from the stars escape. Thus, black holes may have helped make the universe transparent.”

Kaaret and his team focused on a galaxy called Tol 1247-232, located some 600 million light years from Earth, one of only three nearby galaxies from which ultraviolet light has been found to escape. In May 2016, using an Earth-orbiting telescope called Chandra, the researchers saw a single X-ray source whose brightness waxed and waned and was located within a vigorous star-forming region of Tol 1247-232.

The team determined it was something other than a star.

“Stars don’t have changes in brightness,” Kaaret says. “Our sun is a good example of that.

"To change in brightness, you have to be a small object, and that really narrows it down to a black hole,” he says.

But how would a black hole, whose intense gravitational pull sucks in everything around it, also eject matter?

The quick answer is no one knows for sure. Black holes, after all, are hard to study, in part because their immense gravitational pull allows no light to escape and because they’re embedded deep within galaxies.

Recently, however, astronomers have offered an explanation: The jets of escaping matter are tapping into the accelerated rotational energy of the black hole itself.

Imagine a figure skater twirling with outstretched arms. As the skater folds her arms closer to her body, she spins faster. Black holes operate much the same way: As gravity pulls matter inward toward a black hole, the black hole likewise spins faster. As the black hole’s gravitational pull increases, the speed also creates energy.

“As matter falls into a black hole, it starts to spin and the rapid rotation pushes some fraction of the matter out,” Kaaret says. “They’re producing these strong winds that could be opening an escape route for ultraviolet light. That could be what happened with the early galaxies.”

Kaaret plans to study Tol 1247-232 more closely and find other nearby galaxies that are leaking ultraviolet light, which would help corroborate his theory.

Citizen scientists uncover a cold new world near sun

Backyard Worlds volunteers make first discovery: A cold, close brown dwarf

A new citizen-science tool released earlier this year to help astronomers pinpoint new worlds lurking in the outer reaches of our solar system has already led to a discovery: a brown dwarf a little more than 100 light years away from the Sun. Just six days after the launch of the Backyard Worlds: Planet 9 website in February, four different users alerted the science team to the curious object, whose presence has since been confirmed via an infrared telescope. Details were recently published in the Astrophysical Journal Letters.

“I was so proud of our volunteers as I saw the data on this new cold world coming in,” said Jackie Faherty, a senior scientist in the American Museum of Natural History’s Department of Astrophysics and one of Backyard World’s researchers. “It was a feel-good moment for science.”

The Backyard Worlds project lets anyone with a computer and an internet connection flip through images taken by NASA’s Wide Field Infrared Survey Explorer (WISE) spacecraft. If an object is close enough to Earth, it will appear to “jump” when multiple images taken of the same spot in the sky a few years apart are compared. The goal for Backyard Worlds volunteers–of which there are more than 37,000–is to flag the moving objects they see in these digital flipbooks for further investigation by the science team. So far, volunteers have classified more than 4 million flipbooks.

Days after the Backyard Worlds website debuted on February 15, Bob Fletcher, a science teacher in Tasmania, identified a very faint object moving across the WISE images. It was soon also flagged by three other citizen scientists from Russia, Serbia, and the United States.

After some initial investigation by the research team, which originally called the object “Bob’s dwarf,” Faherty was awarded time on NASA’s Infrared Telescope Facility in Hawaii, where she confirmed that it was a previously unknown brown dwarf just a few hundred degrees warmer than Jupiter. The authors say that sky surveys had missed this object because it’s too faint. All four volunteers are co-authors on the scientific paper announcing the discovery.

Brown dwarfs, sometimes called “failed stars,” are spread throughout the Milky Way. They lack enough mass to sustain nuclear fusion but they are hot enough to glow in the infrared range of the light spectrum.
“Brown dwarfs are strikingly similar to Jupiter so we study their atmospheres in order to look at what weather on other worlds might look like,” said Jonathan Gagné, a Backyard Worlds team member from the Carnegie Institution for Science.

Although the Backyard Worlds research team hopes to find the infamous Planet 9 hiding in our own solar system, these brown dwarfs are also exciting discoveries.

“It’s possible that there is a cold world closer than what we believe to be the closest star to the Sun,” Faherty said. “Given enough time, I think our volunteers are going help to complete the map of our solar neighborhood.”


Slow Light

It takes a photon just eight minutes to traverse the 150 million kilometres between the Earth and the Sun, but a photon in the core of the Sun will travel only thirteen centimetres in that same time.

Stars are essentially huge nuclear fusion factories, forging elements in their incredibly hot cores. X-rays and Gamma rays are emitted as a byproduct of this process, but their movements to the surface aren’t straight or easy—the journey could take them tens of thousands of years. The Sun’s core is so dense that the radiation continually hits other atoms, travelling only a few millimetres before being absorbed and then re-emitted over and over again, zig-zagging its way out like a drunk staggering home.

Slowly, the photons work their way up through various layers, including the radiative zone, where they are remitted at longer wavelengths and therefore gradually converted to visible light. Then they pass through the convective zone where the photons are absorbed by gas, heating it up and making it rise towards the surface where it creates the boiling effect we recognise so well.

Finally, after travelling 695,000 kilometres from the core, the photons burst free of the photosphere and into the vacuum of space, racing off at the ordinary speed of light: 300,000 kilometres per second.

It might seem like we’re getting fresh, new light down here on Earth, but in reality our skin is being kissed by photons born eons ago.

(Image Credit: NASA)