Daily Archives: June 7, 2017

Einsteins theory of general relatively changed the way scientists look at the universe. The presence of mass bends spacetime like a bowling ball depressing a mattress, causing light to curve as it travels through these depressions on its way to Earth. In 1919, Sir Arthur Eddington confirmed this effect by measuring the deflection of background stars caused by our Sun during a total solar eclipse. Nearly a century later, astronomers have used the Hubble Space Telescope (HST) to measure this effect caused by a star outside our solar system for the first time.

This groundbreaking result was announced today at the 230th Meeting of the American Astronomical Society by Kailash Sahu of the Space Telescope Science Institute. Sahus team used HST to capture the deflection of light from a background star as a white dwarf, the remnant core of a star once like our Sun, passed in front of it as seen from Earth. Although this deflection was tiny about 1,000 times smaller than the deflection measured by Eddington in 1919 the precision achievable with Hubble allowed astronomers to see it clearly. From the deflection, they were able to measure the mass of the white dwarf, called Stein 2051B, in a new way that independently confirms the theoretical mass-radius relationship for white dwarfs. This is good news, because the mass-radius relationship is the foundation for astronomers use of these objects as standard distance indicators in cosmology. The work will appear this month in the journal Science.

To find a suitable pair of stars to accomplish this task, Sahus team first combed through a catalog of 10,000 stars with large proper motions, or movements on the sky as seen from Earth. Based on the motions of these stars, the team projected the stars positions forward in time to find a pair that would pass close enough to each other (when projected on the sky, not in physical space) to produce a bend in starlight measurable with HST.

Their choice: Stein 2051B, a white dwarf 17 light-years from Earth. According to the teams calculations, Stein 2051B would pass in front of a distant background star, about 5,000 light-years away, causing the background starlight to bend by 2 milliarcseconds. In more understandable terms, seeing that bend would be like trying to watch an insect crawl across the face of a quarter from a distance of about 1,500 miles (2,400km).

The team enlisted Hubble to observe the stars over eight epochs, or points in time, with observations taken in the time leading up to, during, and after the event, which occurred in March 2014. And, indeed, they did observe a deflection of the background light as the white dwarf passed in front of the distant source.

This work represents two firsts in astronomy. One, its the first time a deflection due to general relativity has been measured using a star other than our Sun. And two, as Sahu explained during the press conference, measuring the mass of Stein 2051B is the first clean test for [the] mass-radius relationship.

The mass-radius relationship for white dwarfs leads to a limit called the Chandrasekhar limit. If a white dwarf accumulates mass past this limit (by stealing it off a binary companion), it will explode as a supernova, which can be seen from vast distances and can be used by astronomers to measure very large distances accurately. But if this relationship is different than we currently understand it, it would affect distance measurements based on white dwarf supernovae.

The rest is here:

Astronomers weigh a white dwarf using gravitational lensing - Astronomy Magazine

Cool stars have really come into their own lately, especially as discoveries of their planetary systems increase (think TRAPPIST-1 and Proxima Centauri). But despite their relatively cool nature, these stars can put out intense flares that might affect the planets haplessly circling them. The role of such flares remains unknown but maybe not for long, now that a team of astronomers has begun building a database of dwarf star flares from high-precision data obtained by the Galaxy Evolution Explorer (GALEX) mission.

The database was introduced Tuesday morning at the 230th Meeting of the American Astronomical Society by Chase Million of Million Concepts. Million is the leader of a project called gPhoton, which has undertaken the effort to reprocess data taken by GALEX, which recorded the sky in ultraviolet (UV) light. Thus far, the team has examined more than 100 terabytes of data, looking for flares from red dwarf stars. Although these stars are normally unremarkable in the UV bands, the flares they emit cause them to brighten and become noticeable at these wavelengths, if only for a short time. The foundation of this work is the observation that the sky changes rapidly, said Million during the press conference in Austin, Texas.

While large flares are easier to record, smaller flares have also been seen and theyre predicted to occur more frequently. Its these smaller flares that Million and his colleagues are looking to identify, thanks to the remarkably high precision (5 thousandths of a second) of the data taken by GALEX. Finding these rapid flares is now possible with the help of gPhoton, which allows astronomers to unlock that very short time domain data and study very fast variables with archival data, he said.

The gPhoton database is now a trillion photons strong and 1.2 terabytes in size. Its currently comprised of 10,000 m-dwarf stars with known distances, and each star has its own light curve (a measurement of the amount of light it emits over time). From these light curves, the team has already identified 100 to 200 small flares, each about a minute in length, at energies that havent really been measured before, said Million.

And these flares could have serious implications for planets around these cool stars. Habitable planets are closer to cooler stars and cooler stars, we know, have a lot of these flares Even though small flares are small, because the planets are closer, they will have more of an impact on the habitability of those planets.

As Scott Fleming of the Space Telescope Science Institute explained in an accompanying press release, What if planets are constantly bathed by these smaller, but still significant, flares? There could be a cumulative effect.

Concluding his presentation, Million said, Im intentionally vague. This means something I really do not know. It may be that flares strip away the atmospheres and maybe that they irradiate the surfaces. Theres even a recent preprint where they say some amount of flare activity may be necessary for prebiotic chemistry. I dont know, but Im really excited to get this result out so that other people can tell me what it means.

Read more:

Do stellar flares damage exoplanets? - Astronomy Magazine

The term gravitational lensing has become pretty commonplace. This effect, which occurs when light from a background object, such as a galaxy, is magnified and brightened when it encounters a massive gravitational field, say from a galaxy cluster, on its way to Earth. Gravitational lensing can make otherwise impossible-to-see objects visible, and offers a window into the very distant universe. It also turns out, gravitational lensing is responsible for many, if not all, of the brightest infrared galaxies we see in the sky.

James Lowenthal of Smith College made the announcement Tuesday afternoon at a press conference during the 230th Meeting of the American Astronomical Society, which is taking place in Austin, Texas. Lowenthal and his collaborators are interested in studying galaxies called ultra-luminous infrared galaxies, or ULIRGS, which are undergoing huge booms of star formation in the faraway universe. However, star formation produces dust as a natural result; because these galaxies are dusty, much of their optical light is hidden and reprocessed by the dust, which re-emits the light at longer wavelengths: the infrared. Understanding why these galaxies are undergoing such intense star formation is vital to creating a more complete picture of galaxy evolution over time.

Lowenthals group began with data taken by the Planck satellite, which was launched to map the cosmic microwave background left over from the Big Bang. But because the satellite observed the sky in infrared and submillimeter wavelengths, it was also able to spot bright infrared galaxies. From this data, Lowenthals team assembled a sample of 31 of the brightest sources some of the very brightest infrared galaxies in the universe, Lowenthal said during the press conference. These sources are star-forming galaxies that existed between 8 and 11.5 billion years ago, churning out stars at a rate 1,000 or more times that of the Milky Ways current star formation rate (about one solar mass per year). In fact, theyre so active that theyre not just ULIRGS, theyre 10 or 100 times the ULIRG threshold, said Lowenthal. They really are the most luminous objects that we know of.

They team followed up their sample by looking at data taken with the ESA's Herschel Space Observatory and the Very Large Array. Finally, they used the Large Millimeter Telescope to observe their galaxy sample to measure their distances.

But because observing in longer wavelengths reduces the resolution, or sharpness, of the data, the team was still missing information about the nature of these galaxies. In particular, it was still difficult to tell why they were forming stars at such high rates. So they next turned to the Hubble Space Telescope (HST); while ULIRG galaxies dont normally put out a lot of optical light because its obscured by dust, these galaxies are so extreme that they still emit enough for Hubble to pick it up.

Now, the first 11 of 31 have been imaged by HST, and the result is already astounding: These galaxies are all gravitationally lensed. They knocked our socks off, Lowenthal said. This has been a treasure box, a jewel box of cool new images. And one after another, you see gravitational lenses galore.

What does that mean? These galaxies are all made brighter and bigger by the presence of galaxy clusters containing huge amounts of mass between the ULIRG and Earth. At least eight of the images show Einstein rings, an artifact of lensing that can smear the distant galaxy into a circular shape as a result of the viewing geometry. Lowenthal likened it to looking at a candle through a wine glass held longwise. If the glass is tilted just right, the image of the candle will smear out into a circle.

We have added significantly to the total list of known gravitational lenses without even trying, Lowenthal said. We did not set out to find gravitational lenses. We set out to study distant, dusty starburst galaxies. But it turns out the brightest ones are all gravitationally lensed.

These lensed images also show dramatically more detail than images captured with other instruments. And despite the distorted images created by the lenses, Lowenthals team can use these new, clearer images to reconstruct the galaxies to, he said, unscramble the true shape and nature of the background galaxies. And we can do it with better precision than we could before.

This unprecedented detail will allow astronomers to peer deeper into the mechanisms responsible for these galaxies star formation on smaller scales within the galaxy itself, as small as 10 to 100 light-years across. Currently, there are two theories behind such huge bursts of star-forming activity in the distant universe: mergers between galaxies that excite material into forming stars, and cold gas flooding into galaxies from the intergalactic medium to feed star formation. In nearby galaxies, the former is responsible, but in these more distant galaxies, the question remains. The information needed to discern between the two ideas might be found inside these gravitationally lensed galaxies.

Lowenthal concluded the press conference by showing the attendees a sneak peek of the newest image, which hed received while at the conference. And, just as the others in his sample: Its another one, he said, as the image appeared on the screen to confirm it. Its another spectacular gravitational lens.

More:

Gravitational lenses reveal the universe's brightest galaxies - Astronomy Magazine

Its a freezing January night, at 3200-meter above sea level, in southwest China. The wind sweeps across the mountaintop from east to west, reddening bare fingers in seconds. But looking at the stars above, youll easily forget where you are.

About 26 miles away from Lijiang, Yunnan, the Lijiang observatory is within a village called Gao Mei Gu. Gao Mei Gu means a place higher than the sky in the language of Naxi people, the only ethnic group in China that has maintained traditions of a matrilineal clan. While Lijiang is famous for its ancient city and tourism, Gao Mei Gu is famous for its starry sky.

Its the same starry sky that has attracted some businessman to drive across half of the country about 1200 miles just for an overnight camping every winter, tent and telescope in his BMW trunk. And its the same starry sky that stopped a female officer during a tour, laying herself down on the ground and staring at the heaven-like view despite the coldness. Many amateur astronomers and enthusiasts were also moved to tears by the starry sky.

The Lijiang Observatory hosts the most productive research optical telescope in China, the observatorys director, Jinming Bai, wrote in the preface of its 2016 annual report. The optical telescope hes referring to is the 2.4m telescope. About 30 percent of active galactic nuclei identified in the world were viewed at this telescope, as well as 10 percent of the supernovae, according to Liang Chang, the chief optical engineer at the Observatory. The 2.4m telescope was also used to look for high-redshift quasars, important celestial bodies for studying universes early days and the evolution of black holes. In a 2016 Astrophysical Journal article surveying 75 high redshift quasars, researchers were able to find 36 of them with the 2.4m telescope.

Some special features of the 2.4m telescope make such discoveries possible. For example, the telescope is capable of creating both spectrographs and visual images. Its 2.3-ton primary mirror is made from materials with near-zero thermal expansion, and the mirrors position can be auto-adjusted by air pressure for precise observation. On its Cassegrain focus, a fast instrument change system switches different instruments in less than 30 seconds, thus maximizing the telescopes observation time.

When I visit the control room during a winter night researchers on shift are observing astronomical bodies that might be supernovae. These supernovae candidates are not confirmed yet, explains a PhD student as he zooms in to show the redshift of star of interest. Because they are too close to the galaxies around them, its impossible to tell the supernovae and the galaxies apart not by direct imaging. The good news is that supernovae and galaxies have vastly different spectrograph presentations. So spectrographs collected by the 2.4m telescope will be used to disentangle these two groups of celestial bodies and to see if there are supernovae hiding insides their surrounding galaxies.

The perspectives of those young astronomers at the Lijiang Observatory are somewhat unique too. They conquer technical and financial difficulties with innovations, sacrificing family time and health by devoting themselves to this high altitude observatory in their 30s. Not only driven by an academic passion, they also have a sense of mission. They aspire to make Chinas astronomy research abreast with the worlds best.

Recently, a 12-meter Optical/Infrared Telescope has been listed as a key project of Chinas Thirteenth Five-Year Plan. The chief optical engineer, Chang, says while its ok for China to aim at building the next biggest telescopes, China needs more medium optical telescopes in the diameter range of 3-5 meters. It would mean lower investment and more scientific output. An 8-meter optical telescope in design, the Chinese Giant Solar Telescope, is expected to cost $90 million.

Yufeng Fan, engineer in chief of the Lijiang Observatory, agrees on the usefulness of optical telescopes with medium size. And Fan adds that the Lijiang observatory always looks forward to having more fresh blood to help with the teams research.

As we step out of the dome, clouds from the east have covered almost all stars, and the nights observation has to end. Its past 11pm and our guide Yuxin Xin is still energetic. Staying up late is an old habit of astronomers observing the sky at night, Xin says. On the drive back to downtown, we talk about his work, future of astronomy and unsolved mysteries. To him, he says, its really amazing that the extreme big and the extreme small of the universe are actually in the same form: Planets orbiting the sun is somewhat like electrons orbiting the nucleus.

I think of the image I saw on one of the monitors in the telescopes control room: two swirling distant galaxies in a long and slow process of merging together. Isnt that image somewhat similar to the image of two single-celled organisms merging into a multicellular one under the microscope? Not usually familiar to us lay people, those two images are both beauties at another scale, wonders in different corners of the world.

Read more:

An observatory higher than the sky | Astronomy.com - Astronomy Magazine

This artists concept shows planet KELT-9b orbiting its host star, KELT-9. It is the hottest gas giant planet discovered so far. Credit: NASA/JPL-Caltech

A newly discovered Jupiter-like world is so hot, its being vaporized by its own star.

With a dayside temperature of more than 7,800 degrees Fahrenheit (4,600 Kelvin), KELT-9b is a planet that is hotter than most stars. But its blue A-type star, called KELT-9, is even hotter in fact, it is probably unraveling the planet through evaporation.

This is the hottest gas giant planet that has ever been discovered, said Scott Gaudi, astronomy professor at The Ohio State University in Columbus, who led a study on the topic. He worked on this study while on sabbatical at NASAs Jet Propulsion Laboratory, Pasadena, California. The unusual planet is described in the journal Nature and at a presentation at the American Astronomical Society summer meeting this week in Austin, Texas.

KELT-9b is 2.8 times more massive than Jupiter, but only half as dense. Scientists would expect the planet to have a smaller radius, but the extreme radiation from its host star has caused the planets atmosphere to puff up like a balloon.

Because the planet is tidally locked to its star as the moon is to Earth one side of the planet is always facing toward the star, and one side is in perpetual darkness. Molecules such as water, carbon dioxide and methane cant form on the dayside because it is bombarded by too much ultraviolet radiation. The properties of the nightside are still mysterious molecules may be able to form there, but probably only temporarily.

Its a planet by any of the typical definitions of mass, but its atmosphere is almost certainly unlike any other planet weve ever seen just because of the temperature of its dayside, Gaudi said.

The KELT-9 star is only 300 million years old, which is young in star time. It is more than twice as large, and nearly twice as hot, as our Sun. Given that the planets atmosphere is constantly blasted with high levels of ultraviolet radiation, the planet may even be shedding a tail of evaporated planetary material like a comet.

KELT-9 radiates so much ultraviolet radiation that it may completely evaporate the planet, said Keivan StasSun, a professor of physics and astronomy at Vanderbilt University, Nashville, Tennessee, who directed the study with Gaudi.

But this scenario assumes the star doesnt grow to engulf the planet first.

KELT-9 will swell to become a red giant star in a few hundred million years, said Stassun. The long-term prospects for life, or real estate for that matter, on KELT-9b are not looking good.

The planet is also unusual in that it orbits perpendicular to the spin axis of the star. That would be analogous to the planet orbiting perpendicular to the plane of our solar system. One year on this planet is less than two days.

KELT-9b is nowhere close to habitable, but Gaudi said theres a good reason to study worlds that are unlivable in the extreme.

As has been highlighted by the recent discoveries from the MEarth collaboration, the planet around Proxima Centauri, and the astonishing system discovered around TRAPPIST-1, the astronomical community is clearly focused on finding Earth-like planets around small, cooler stars like our Sun. They are easy targets and theres a lot that can be learned about potentially habitable planets orbiting very low-mass stars in general. On the other hand, because KELT-9bs host star is bigger and hotter than the Sun, it complements those efforts and provides a kind of touchstone for understanding how planetary systems form around hot, massive stars, Gaudi said.

The KELT-9b planet was found using one of the two telescopes called KELT, or Kilodegree Extremely Little Telescope. In late May and early June 2016, astronomers using the KELT-North telescope at Winer Observatory in Arizona noticed a tiny drop in the stars brightness only about half of one percent which indicated that a planet may have passed in front of the star. The brightness dipped once every 1.5 days, which means the planet completes a yearly circuit around its star every 1.5 days.

Subsequent observations confirmed the signal to be due to a planet, and revealed it to be what astronomers call a hot Jupiter the kind of planet the KELT telescopes are designed to spot.

Astronomers at Ohio State, Lehigh University in Bethlehem, Pennsylvania, and Vanderbilt jointly operate two KELTs (one each in the northern and southern hemispheres) to fill a large gap in the available technologies for finding exoplanets. Other telescopes are designed to look at very faint stars in much smaller sections of the sky, and at very high resolution. The KELTs, in contrast, look at millions of very bright stars at once, over broad sections of sky, and at low resolution.

This discovery is a testament to the discovery power of small telescopes, and the ability of citizen scientists to directly contribute to cutting-edge scientific research, said Joshua Pepper, astronomer and assistant professor of physics at Lehigh University in Bethlehem, Pennsylvania, who built the two KELT telescopes.

The astronomers hope to take a closer look at KELT-9b with other telescopes including NASAs Spitzer and Hubble space telescopes, and eventually the James Webb Space Telescope, which is scheduled to launch in 2018. Observations with Hubble would enable them to see if the planet really does have a cometary tail, and allow them to determine how much longer that planet will survive its current hellish condition.

Thanks to this planets star-like heat, it is an exceptional target to observe at all wavelengths, from ultraviolet to infrared, in both transit and eclipse. Such observations will allow us to get as complete a view of its atmosphere as is possible for a planet outside our solar system, said Knicole Colon, paper co-author who was based at NASA Ames Research Center in Californias Silicon Valley during the time of this study.

Visit link:

Astronomers find planet hotter than most stars - Astronomy Now Online