KREUZADER (Posts tagged astronomy)

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Extinction and the Dimming of KIC 8462852 “ To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star over a wide wavelength range from the UV to the mid-infrared from October 2015 through December 2016,...

Extinction and the Dimming of KIC 8462852

To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star over a wide wavelength range from the UV to the mid-infrared from October 2015 through December 2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the long-term fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period reported is 22.1 +- 9.7 milli-mag/yr in the Swift wavebands, with amounts of 21.0 +- 4.5 mmag in the groundbased B measurements, 14.0 +- 4.5 mmag in V, and 13.0 +- 4.5 in R, and a rate of 5.0 +- 1.2 mmag/yr averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at >= 3 sigma by three different observatories operating from the UV to the IR. The presence of long-term secular dimming means that previous SED models of the star based on photometric measurements taken years apart may not be accurate. We find that stellar models with T_{eff} = 7000 - 7100 K and A_V ~ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the near-simultaneous Spitzer photometry at 3.6 and 4.5 microns, although a longer wavelength excess from a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of the fading favors a relatively neutral color (i.e., R_V >= 5, but not flat across all the bands) compared with the extinction law for the general ISM (R_V = 3.1), suggesting that the dimming arises from circumstellar material.

Source: arxiv.org
astronomy kic 8462852 boyajian's star
Eclipse Hunter Reveals the Science That Can Only Be Done in the Dark “On Aug. 21, a total solar eclipse will be visible from a narrow ribbon of land — the “path of totality,” which stretches across the United States from Oregon to South Carolina. It...

Eclipse Hunter Reveals the Science That Can Only Be Done in the Dark

On Aug. 21, a total solar eclipse will be visible from a narrow ribbon of land — the “path of totality,” which stretches across the United States from Oregon to South Carolina. It will be the first total eclipse visible from the 48 contiguous states since 1979. These events are often described as once-in-a-lifetime experiences, but for Jay Pasachoff, they’ve come more often than that. He’s seen 33 total solar eclipses, and another 32 if you count partial eclipses and annular eclipses, in which the sun briefly looks like a ring or doughnut.

Pasachoff, an astronomer at Williams College in Massachusetts, will view the event in Salem, Oregon, accompanied by a group of students and thousands of pounds of equipment. That’s because even in this age of space probes and orbiting telescopes, there’s still a good deal of science that can be done from the ground during those brief moments in the moon’s shadow — science that, in fact, can be done only during a total solar eclipse.

Source: quantamagazine.org
astronomy eclipse
Boyajian’s Star Update: “At the time TFN started taking observations (blue points), the flux was way down(!!); and it continued to change quite significantly over the course of a couple hours. At the end of the TFN visibility window, it had returned...

Boyajian’s Star Update:

At the time TFN started taking observations (blue points), the flux was way down(!!); and it continued to change quite significantly over the course of a couple hours.  At the end of the TFN visibility window, it had returned to the same level of brightness from the previous day, and this continued for the time it was observed at OGG.  This short term variability was also independently detected by colleagues observing at the TJO telescope in Spain, so the chances are very good that it is real (not a problem with the data).  Unfortunately what we saw didn’t last long, only a couple of hours. But we don’t have any coverage just before it, from 94.1-94.3 on this x-axis, so we could only guess to what happened during that time: did we catch it on the way up from a quick, big drop, or was the event more shallow and gradual?        

I have been reminded that its probably a good idea to note that the data shown here are normalized to unity.  Normalizing to unity shows the depths of the dips plus any long term dimming trends that may be occurring, which is what we care about anyway (the total amount of stuff is between us and the star). We will need a lot more data (when the star is not dipping) to address this long term dimming properly, and at this point its best to avoid such speculation.  

Source: wherestheflux.com
astronomy space kic 8462852 boyajian's star
“A new analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of stars around the supermassive black hole at the centre of the Milky Way may show the subtle effects predicted by Einstein’s general theory of...

A new analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of stars around the supermassive black hole at the centre of the Milky Way may show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of the star S2 is deviating slightly from the path calculated using classical physics. This tantalising result is a prelude to much more precise measurements and tests of relativity that will be made using the GRAVITY instrument as star S2 passes very close to the black hole in 2018.

Source: eso.org
astrophysics astronomy general relativity black hole space
“Astronomers have identified the oldest asteroid families and, by process of elimination, the oldest intact asteroids in the main belt. A team including SwRI scientists developed a technique to identify ancient asteroid families that have drifted...

Astronomers have identified the oldest asteroid families and, by process of elimination, the oldest intact asteroids in the main belt. A team including SwRI scientists developed a technique to identify ancient asteroid families that have drifted apart. Asteroid surfaces heat up during the day (as illustrated by this image) and cool down at night, giving off radiation that can act as a sort of mini-thruster. This force can cause asteroids to drift widely over time, making it difficult to identify families of fragments leftover after asteroid collisions eons ago.

Source: swri.org
asteroid astronomy
New Simulations Could Help in Hunt for Massive Mergers of Neutron Stars, Black Holes“Now that scientists can detect the wiggly distortions in space-time created by the merger of massive black holes, they are setting their sights on the dynamics and...

New Simulations Could Help in Hunt for Massive Mergers of Neutron Stars, Black Holes

Now that scientists can detect the wiggly distortions in space-time created by the merger of massive black holes, they are setting their sights on the dynamics and aftermath of other cosmic duos that unify in catastrophic collisions.

Working with an international team, scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed new computer models to explore what happens when a black hole joins with a neutron star – the superdense remnant of an exploded star.

[…]

In separate papers published in a special edition of the scientific journal Classical and Quantum Gravity, Berkeley Lab and other researchers present the results of detailed simulations.

One of the studies models the first milliseconds (thousandths of a second) in the merger of a black hole and neutron star, and the other details separate simulations that model the formation of a disk of material formed within seconds of the merger, and of the evolution of matter that is ejected in the merger.

Source: newscenter.lbl.gov
astrophysics astronomy gravitational astronomy gravitational waves physics
New Insights into Long-Period Comets“Comets that move regularly into the inner system are found to be, on average, as much as four times smaller than long-period comets, those moving only rarely near the Sun. Moreover, there are seven times more...

New Insights into Long-Period Comets

Comets that move regularly into the inner system are found to be, on average, as much as four times smaller than long-period comets, those moving only rarely near the Sun. Moreover, there are seven times more long-period comets in the size range of one kilometer in diameter and above than had previously been thought. In the eight months of the study period, three to five times more long-period comets were observed moving in the vicinity of the Sun than had been predicted.

[…]

Co-author Amy Mainzer (JPL), principal investigator of the NEOWISE mission, points out that, traveling much faster than asteroids, long-period comets like these, many of them quite large, have to be factored into our analyses of impact risk. We’re developing an extensive catalog of near-Earth objects, but a long-period comet dislodged from the Oort Cloud, moving faster than any near-Earth asteroid, poses a risk that is badly in need of assessment.

yikes - damocloids in particular are the worst - very difficult to see in advance, probably relatively large, and moving at very high relative velocity to Earth

Source: centauri-dreams.org
planetary defense space astronomy
“The analysis, posted on DES’s website today and based on observations of 26 million galaxies in a large swath of the southern sky, tweaks estimates only a little. It draws the pie chart of the universe as 74 percent dark energy and 21 percent dark...

The analysis, posted on DES’s website today and based on observations of 26 million galaxies in a large swath of the southern sky, tweaks estimates only a little. It draws the pie chart of the universe as 74 percent dark energy and 21 percent dark matter, with galaxies and all other visible matter — everything currently known to physicists — filling the remaining 5 percent sliver.

Source: quantamagazine.org
astronomy space cosmology astrophysics
Dark matter is missing from young galaxies“These rotation curves showed something unexpected: rather than remaining steady, velocities quickly tailed off as measurements moved away from the center of the galaxies. In fact, the curves looked a lot...

Dark matter is missing from young galaxies

These rotation curves showed something unexpected: rather than remaining steady, velocities quickly tailed off as measurements moved away from the center of the galaxies. In fact, the curves looked a lot like what you’d expect based on the description above, if there were no dark matter around. Comparisons with models of galaxy behavior confirmed and quantified this idea: the curves could be reproduced using models that had a minimal dark matter component.

The authors checked a number of alternative explanations, like the gravitational influence of nearby galaxies or orbiting dwarf galaxies, but neither of these appeared to be a major factor. The drop in rotational velocity was also symmetric around the galaxy, which would seem to rule out localized influences. When the authors added local (and thus more current) galaxies to the analysis, the analysis showed that the faction of dark matter in galaxies seems to go down as you go further back in time.

It might be tempting to view this all as a problem for the idea of dark matter. But it’s worth noting that the primary alternatives to dark matter, modified versions of gravity, wouldn’t explain the situation either, as they suggest gravity changes over distance but not time.

The authors of the new paper see a number of possible explanations. One is that the early galaxies are very gas-rich, and these clouds of gas can experience local instabilities or collisions. This could cause the regular matter in the inner galaxy to compact, resulting in a normal-matter-dominated portion of the galaxy. The other possibility is that rather than forming the seeds of galaxies, dark matter starts off rather diffuse and takes time to form a disk-like structure that mirrors that of the visible galaxy. Either of these would explain the apparent matter dominance.

Source: Ars Technica
astrophysics space astronomy cosmology
How the discovery of a hot Jupiter’s stratosphere could help the search for life on other planets“The planet, described in a study published today in Nature, is called WASP-121b. It belongs to a class of exoplanets called hot Jupiters — worlds that...

How the discovery of a hot Jupiter’s stratosphere could help the search for life on other planets

The planet, described in a study published today in Nature, is called WASP-121b. It belongs to a class of exoplanets called hot Jupiters — worlds that are so big and hot that they are fairly easy to study, thus allowing astronomers to hone their skills and confirm their theories. Today’s discovery confirms what astronomers suspected: super hot gas giants outside our Solar System can have a stratosphere.

WASP-121b is massive — nearly twice the size of our Jupiter. And because it orbits much closer to its host star than Mercury orbits around the Sun, its atmosphere heats up to more than 4,500 degrees Fahrenheit. (At that temperature, you could boil iron.) Using NASA’s Hubble Space Telescope, the researchers were able to detect glowing water molecules in the planet’s atmosphere, a clear signal that WASP-121b has a stratosphere. What exactly is causing the stratosphere is more of a mystery, but it could be gases like vanadium oxide and titanium oxide, which are believed to act like the ozone on Earth, the study says.

[…]

Worlds like WASP-121b are way too hot to possibly host any kind of life as we know it — whether or not they have a stratosphere. But studying them is still key: it allows researchers to test their theories and learn more about the underlying physics. “They are a first step towards honing our skills, developing our tools, getting ready for the things that are more Earth-like,” says Kevin Heng, the director of the Center for Space and Habitability at the University of Bern. “This is the first step in a long road.” 

Source: theverge.com
astronomy space
Astronomers find that the sun’s core rotates four times faster than its surface““The most likely explanation is that this core rotation is left over from the period when the sun formed, some 4.6 billion years ago,” said Roger Ulrich, a UCLA professor...

Astronomers find that the sun’s core rotates four times faster than its surface

“The most likely explanation is that this core rotation is left over from the period when the sun formed, some 4.6 billion years ago,” said Roger Ulrich, a UCLA professor emeritus of astronomy, who has studied the sun’s interior for more than 40 years and co-author of the study that was published today in the journal Astronomy and Astrophysics. “It’s a surprise, and exciting to think we might have uncovered a relic of what the sun was like when it first formed.”

The rotation of the solar core may give a clue to how the sun formed. After the sun formed, the solar wind likely slowed the rotation of the outer part of the sun, he said. The rotation might also impact sunspots, which also rotate, Ulrich said. Sunspots can be enormous; a single sunspot can even be larger than the Earth.

Source: newsroom.ucla.edu
astrophysics astronomy sun
Are Astronomers on the Verge of Finding an Exomoon?“This morning David and I put out a paper on the arXiv that represents the culmination of years of work searching for the signature of exomoons in the population of stars examined by the Kepler...

Are Astronomers on the Verge of Finding an Exomoon?

This morning David and I put out a paper on the arXiv that represents the culmination of years of work searching for the signature of exomoons in the population of stars examined by the Kepler Mission. After carefully analyzing an ensemble of the highest quality planetary transit signals, we have determined that exomoons appear to be quite rare in the inner regions of star systems (regions of space close to the host star). This finding was both remarkable and, frankly, a bit disappointing.

[…]


In any case, there was another result in our paper that may make a considerably larger splash, which you may have even read about in the news, or soon will: We announced our identification of a single exomoon candidate, indeed the strongest candidate we’ve seen in the five year history of the Hunt for Exomoons with Kepler (HEK) collaboration. The system, Kepler-1625 b, has withstood a host of preliminary tests aimed at ruling out the presence of a moon, and our proposal to observe this system with the Hubble Space Telescope was recently accepted. We are thrilled to get the chance to observe with Hubble, and hope that the observation will confirm our suspicion unambiguously that this is a genuine exomoon detection, which would be the first of its kind.


more:

Source: blogs.scientificamerican.com
astronomy space