Tag: astronomy

Quasars that shut off

8:37 am

The uncertainty of science: Astronomers have discovered a class of quasars that suddenly turn off, something that no theory had predicted possible.

LaMassa, an astronomer now at the Space Telescope Science Institute, was mystified. Until that moment in 2014, she, like so many others, had expected quasars to be relatively stagnant. “Then you see these drastic changes within a human lifetime, and it’s pretty cool,” she said.

Confusion turned into excitement, and a hunt began to find more of these oddities. Although less luminous examples had already been seen, astronomers wanted to know if changes as dramatic as the one LaMassa discovered were common. It was no straightforward task, given that surveys tend not to go back and look at objects they have previously observed. But astronomers searched through archived data and discovered 50 to 100 more of what became known as “changing-look quasars.” Some of these have dimmed substantially more than LaMassa’s first example. Others have transitioned in the space of a month or two. And others, after disappearing, have reappeared again.

“It’s clear that the reason we weren’t finding these objects before is that we weren’t looking for them,” said Eric Morganson, an astronomer at the University of Illinois.

The article does a fine job of explaining the whole problem, including outlining the theories now being posited to explain these events. Bottom line: the universe is always more complicated that expected by initial observations.

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Another star found that dims strangely like Tabby’s Star

9:20 am

Astronomers have found a second star that dims in an inexplicable manner, like Tabby’s Star.

Known as VVV-WIT-07, the star appears to be much older and redder than our sun, although the amount of interstellar dust between our solar system and the star’s home closer to the galactic center makes exact classification and distance measurements very difficult. What is certain is that in the summer of 2012, the object’s brightness faded slightly for 11 days, then plummeted over the following 48 days, suggesting that something blocked more than three quarters of the star’s light streaming toward Earth. But what could that “something” be?

According to Eric Mamajek, an astrophysicist at the University of Rochester unaffiliated with the VVV survey, such a profound degree of dimming suggests that a staggeringly large object or group of objects is blocking the light. “It’s got to be over a million kilometers wide, and very dense to be able to block that much starlight,” he says. Mamajek should know: He led the team that discovered J1407, another strange star periodically eclipsed by a planet-sized object thought to boast a massive ring system some 200 times broader than that of Saturn. In this latest case, he says, the strange signals from VVV-WIT-07 could arise from clumps or clouds of material passing between Earth and the star, though he cautioned that the data were preliminary and more observations are required.

Tabetha Boyajian agrees. Boyajian, an astronomer at Louisiana State University, was the lead author for the 2015 paper announcing the strange dimming of KIC 8462852, also known as Tabby’s Star, an unusual object first spotted by NASA’s Kepler Space Telescope. VVV-WIT-07 would have to harbor “a very peculiar kind of dust cloud to make these kinds of dips,” Boyajian says. Boyajian’s study helped spark a surge of public interest in Tabby’s Star because the star’s unusual dimming could be seen as evidence of an alien civilization building an artificial structure that soaked up the star’s light. More conventional explanations include a swarm of comets or fragments from a shattered planet, both of which would create significant clouds of dust and debris that could also occlude the star’s light. But, so far, no simple single explanation fits the complexities of the dimming seen around the star; researchers remain stymied in their attempts to understand the true nature of the strange dimming of Tabby’s Star.

As is usually the case in these cases, the explanation will not be aliens. That it could be, however, is what makes it so intriguing.

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New Wolf-Rayet star discovered 8,000 light years away

10:10 am

Astronomers have discovered a Wolf-Rayet star — the kind of star thought to eventually cause major explosions — 8,000 light years away.

The binary star system, containing a pair of massive ‘Wolf-Rayet’ stars, has been discovered by an international team of researchers, including Professor Paul Crowther from the University of Sheffield, and published in Nature Astronomy.

Wolf-Rayet stars are amongst the hottest stars in the Universe, blast out powerful winds of hot gas, and represent the last stage in the evolution of the most massive stars prior to exploding as a supernova.

Located around 8,000 light years away – half a billion times further away than our Sun – the binary system is surrounded by a gigantic dust cloud. The collision between the winds of the two stars can form dust, which takes on elegant spiral pinwheel shapes as the stars orbit each other.

Expect to see a number of news articles hinting at how this system is a deadly threat to Earth. It is not. For one thing, it is too far away for any supernovae or gamma ray burst to cause serious harm here. Second, it will be a long time before any of that is going to happen.

Wolf-Rayet stars however are rare, and being able to study them helps astronomers better understand the life and death of stars. Having another so relatively close is a boon to astronomers.

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Computer model suggests universe has innumerable exomoons

10:28 am

A supercomputer simulation has shown that ice-giant planets like Uranus and Neptune can have their own dust disk during formation, thus allowing these kinds of planets to also form moons.

“So far it was believed that Uranus and Neptune are too light to form such a disk,” says the astrophysicist. Therefore, it was considered that the moons of Uranus could have formed after a cosmic collision – like our own moon, also a relatively infrequent event as the capture. Now the researchers who are also members of the NCCR PlanetS were able to refute this previous idea. Their extremely complex computer simulations reveal that in fact Uranus and Neptune were making their own gas-dust disk while they were still forming. The calculations generated icy moons in-situ, that are very similar in composition with the current Uranian satellites. From the simulations performed by the supercomputer called “Mönch” at CSCS it is clear that Neptune originally also was orbited by a Uranus-like, multiple moon system, but this must have been wiped out during the capture of Triton.

The new study has a much wider impact on moons in general, than only on our Solar System formation history. “If ice giants can also form their own satellites, that means that the population of moons in the Universe is much more abundant than previously thought,” summarizes Dr.Szulágyi.Ice giants and mini-Neptune planets are often discovered by exoplanet surveys, so this planet mass category is very frequent. “We can therefore expect many more exomoon discoveries in the next decade,” the astrophysicist says.

I actually don’t believe the assumption posited here that scientists previously believed Uranus and Neptune were too light to form disks. I think many astronomers might have believed that, while many others remained unsure, since it is more intuitive to expect such disks to form as these gas giants formed.

Either way, this computer model lends weight to those who believe the universe is littered with planets and moons, everywhere, many of which will exist in the habitable zones of all kinds of stars. These planets and moons might not have life, but they will be places we could live, when we begin colonizing interstellar space.

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Looking at the south pole of the Milky Way

9:36 am

Link here. The link provides instructions for finding the spot in the sky that corresponds to the south pole of the galaxy, pointing in a perpendicular direction away from its center.

No star marks the position. It sits in the faint southern constellation of Sculptor, the sculptor’s studio, hence its identification is intellectual rather than sensorial.

This is the case of the dog that did not bark. The reason there is little to see there is that you will be looking down out of the plane of the galaxy, in a direction with the fewest stars to see. The view is therefore looking out of our galaxy, at intergalactic space, vast and empty.

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Astronomers identify first progenitor star for Type 1C supernovae

3:27 pm

Astronomers have for the first time identified a progenitor star for a Type 1C supernovae.

[The search for supernovae progenitor stars has found] a few pre-supernova stars. But the doomed stars for one class of supernova have eluded discovery: the hefty stars that explode as Type Ic supernovas. These stars, weighing more than 30 times our Sun’s mass, lose their hydrogen and helium layers before their cataclysmic death. Researchers thought they should be easy to find because they are big and bright. However, they have come up empty. Finally, in 2017, astronomers got lucky. A nearby star ended its life as a Type Ic supernova. Two teams of researchers pored through the archive of Hubble images to uncover the putative precursor star in pre-explosion photos taken in 2007. The supernova, catalogued as SN 2017ein, appeared near the center of the nearby spiral galaxy NGC 3938, located roughly 65 million light-years away.

An analysis of the candidate star’s colors shows that it is blue and extremely hot. Based on that assessment, both teams suggest two possibilities for the source’s identity. The progenitor could be a single star between 45 and 55 times more massive than our Sun. Another idea is that it could have been a binary-star system in which one of the stars weighs between 60 and 80 times our Sun’s mass and the other roughly 48 solar masses. In this latter scenario, the stars are orbiting closely and interact with each other. The more massive star is stripped of its hydrogen and helium layers by the close companion, and eventually explodes as a supernova.

As can be seen by the quote above, identifying the star that exploded still leaves much unknown, including whether the star is a single or a binary. Still, they finally have some idea what kind of star erupts in a Type IIC supernovae, which will help constrain the theories for explaining the cause of these explosions.

Note also that this identification will not be confirmed until the supernova itself completely fades in about two years. They might find when that happens that the candidate progenitor is still there, meaning it was not the progenitor of the supernova at all.

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Null result from Spitzer suggests Oumuamua was small

1:43 pm

The uncertainty of science: The inability of the infrared Spitzer Space Telescope to detect the interstellar object Oumuamua as it exited the solar system suggests the object is small.

The fact that ‘Oumuamua was too faint for Spitzer to detect sets a limit on the object’s total surface area. However, since the non-detection can’t be used to infer shape, the size limits are presented as what ‘Oumuamua’s diameter would be if it were spherical. Using three separate models that make slightly different assumptions about the object’s composition, Spitzer’s non-detection limited ‘Oumuamua’s “spherical diameter” to 1,440 feet (440 meters), 460 feet (140 meters) or perhaps as little as 320 feet (100 meters). The wide range of results stems from the assumptions about ‘Oumuamua’s composition, which influences how visible (or faint) it would appear to Spitzer were it a particular size.

The new study also suggests that ‘Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system – a surprising result, according to the paper’s authors.

These results fit the models that explain Oumuamua’s fluctuations in speed as caused by the out gassing of material, like a comet. They also do not contradict the recent hypothesis that the object might have been an alien-built light sail.

The simple fact is that we do not have enough data to confirm any of these theories.

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SuperEarth orbiting Barnard’s Star?

11:18 am

The uncertainty of science: Astronomers have discovered a candidate exoplanet orbiting Barnard’s Star, the closest single star to our solar system and the second closest stellar system after Alpha Centauri.

The planet candidate, named Barnard’s star b (or GJ 699 b), is a super-Earth with a minimum of 3.2 Earth masses. It orbits its cool red parent star every 233 days near the snow-line, a distance where water would be frozen. In the absence of an atmosphere, its temperature is likely to be about -150 ºC, which makes it unlikely that the planet can sustain liquid water on its surface. However, its characteristics make it an excellent target for direct imaging using the next generation of instruments such as NASA’s Wide Field InfraRed Survey Telescope (WFIRST, [3]), and maybe with observations from the ESA mission Gaia [4].

The reason I put a question mark in the headline is that this is not the first time a candidate exoplanet has been proposed to orbit Barnard’s Star. In the 1960s astronomer Peter van de Kemp claimed the star had at least one gas giant orbiting it every 24 years. It was later found that the periodic motion variations he measured were due to “to an artifact of maintenance and upgrade work” at the telescope he was using.

The result above has not been confirmed by other means, so they must list this superEarth as a candidate exoplanet. More observations are necessary to confirm it.

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Neutron star merger caused gravitational wave?

10:17 am

The uncertainty of science: Astronomers now believe that one of the half dozen or so gravitational waves detected by LIGO was likely caused by the merger of two neutron stars.

One of these, GW170817, resulted from the merger of two stellar remnants known as neutron stars. These objects form after stars much more massive than the Sun explode as supernovae, leaving behind a core of material packed to extraordinary densities.

At the same time as the burst of gravitational waves from the merger, observatories detected emission in gamma rays, X-rays, ultraviolet, visible light, infrared and radio waves – an unprecedented observing campaign that confirmed the location and nature of the source.

The initial observations of GW170817 suggested that the two neutron stars merged into a black hole, an object with a gravitational field so powerful that not even light can travel quickly enough to escape its grasp.

While intriguing, this result is uncertain, and based on many assumptions.

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LSST’s giant coating chamber arrives in Chile

2:54 pm

The giant coating chamber that will be used to coat the mirrors for the Large Synoptic Survey Telescope has arrived in Chile.

The Coating Chamber and its associated equipment will share this level with the camera maintenance rooms, the vertical platform lift, and the shipping and receiving area. The Coating Chamber will be used to coat LSST’s mirrors when they arrive on Cerro Pachón, and to re-coat the mirrors periodically during Operations.

LSST will conduct a 10-year survey, and during this period its mirrors will be exposed to the elements each night as the telescope surveys the sky through the open side of the observatory dome. Over time the mirrors will get dusty, and the mirror coatings may develop small blemishes that eventually affect the telescope’s performance. To ensure that LSST continues to collect the sharpest possible images of the night sky, its mirrors will undergo periodic washing and recoating. It’s anticipated that the Primary/Tertiary Mirror (M1M3) will need to be recoated every two years, and the Secondary Mirror (M2) every five years, during the 10-year survey. Both the washing and recoating will be done inside the observatory; special equipment will be used to remove and transport the mirrors from the telescope to the washing station and coating chamber.

LSST will essentially be imaging the entire visible sky nightly, making it possible over time to track sudden events, such as supernovae, as they happen.

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China still struggling to find scientists to run FAST radio telescope

8:32 am

China is still finding it difficult to hire the scientists necessary to run its FAST radio telescope, the largest single dish radio telescope in the world.

And why is that?

For job candidates, the major stumbling blocks often are financial incentives and research independence, researchers told the South China Morning Post. The telescope’s remote location also may give candidates pause.

George Smoot, a Hong Kong University of Science and Technology professor who won the Nobel Prize in physics in 2006, said candidates interested in working in a more developed setting might think twice about spending a lot of time in an area known for its traditional rural villages.

“Another issue is how much the Chinese Academy of Sciences will influence and direct activities there,” Smoot said. “It is an issue to people unless they have some straight link.” [emphasis mine]

It must always be remembered that nothing in China is done without the government’s approval. For western astronomers, used to having a great deal of independence, this fact makes working there somewhat unappealing.

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Danish astronomers question gravitational wave detection

9:23 am

The uncertainty of science: A team of Danish astronomers have questioned the gravitational wave detection achieved in the past few years by the LIGO gravitational wave telescopes.

The details are complex and very much in dispute, and the position of these Danish astronomers is very much in the minority, but their doubts have not been dismissed, and illustrate well the best aspects science. The article also outlines how the physics community and the LIGO scientists have welcomed the skepticism, even as they have doubts about the claims of the Danish astronomers. This is the hallmark of good science, and lends weight to the work at LIGO.

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Head of Webb investigation: Webb was “a step too far”

9:11 am

The head of an investigation panel into the James Webb Space Telescope admitted this week that, though he and the panel fully support the telescope’s completion and launch, he also believes the telescope was too ambitious and “a step too far.”

Speaking at a meeting of the Committee on Astronomy and Astrophysics of the National Academies’ Space Studies Board Oct. 29, Tom Young said that while the mission may ultimately be a success, its difficulties provide lessons as NASA considers future large astronomy missions in the next decadal survey.

“I, personally, have come to the conclusion that JWST had too many inventions, too much risk, and was a step too far,” he said at the end of a presentation about the review board’s work.

Young emphasized that he was neither opposed to JWST being completed nor had doubts it could be done successfully. “There are a group people who are diehard supporters of JWST, and there are others who support it, but they’re really angry at the cost growth and the schedule delays,” he said.

You think? Webb was supposed to cost about $500 million, and launch in 2007. Its budget is now almost $10 billion, and it will not launch before 2021. In the process it has destroyed the entire astronomy program at NASA, preventing the construction of any other space telescopes.

The key question is whether the astronomy community or NASA has learned anything from this disaster. I personally am doubtful, since they are still pushing for WFIRST, a similar big boondoggle that will cost billions and is already overbudget and behind schedule, though it is only in its design stage.

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Early Milky Way collision uncovered by Gaia

12:21 pm

Data from the space telescope Gaia has revealed a Milky Way merger event that occurred about 10 billion years ago.

Using the first 22 months of observations, a team of astronomers led by Amina Helmi, University of Groningen, The Netherlands, looked at seven million stars – those for which the full 3D positions and velocities are available – and found that some 30,000 of them were part of an ‘odd collection’ moving through the Milky Way. The observed stars in particular are currently passing by our solar neighbourhood.

We are so deeply embedded in this collection that its stars surround us almost completely, and so can be seen across most of the sky.

Even though they are interspersed with other stars, the stars in the collection stood out in the Gaia data because they all move along elongated trajectories in the opposite direction to the majority of the Galaxy’s other hundred billion stars, including the Sun. They also stood out in the so-called Hertzprung-Russell diagram – which is used to compare the colour and brightness of stars – indicating that they belong to a clearly distinct stellar population.

The sheer number of odd-moving stars involved intrigued Amina and her colleagues, who suspected they might have something to do with the Milky Way’s formation history and set to work to understand their origins. In the past, Amina and her research group had used computer simulations to study what happens to stars when two large galaxies merge. When she compared those to the Gaia data, the simulated results matched the observations. “The collection of stars we found with Gaia has all the properties of what you would expect from the debris of a galactic merger,” says Amina, lead author of the paper published today in Nature.

At the time, the two galaxies were both probably about the same size, approximately equivalent to the Magellanic Clouds.

Must I mention that there is some uncertainty here? The data is good, and the conclusions seem quite reasonable. At the same time, the data is still somewhat thin. We need a lot more Gaia-type telescopes mapping out the motions and positions of all the stars of the Milky Way in far more detail before the uncertainties here will shrink.

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Timelapse movie of Supernova 1987A’s evolution from 1992 to 2017

9:42 am

Cool movie time! An astronomy graduate student in Toronto has created a movie showing the steady evolution of the shock wave from Supernova 1987A, the first supernova visible to the naked eye since the discovery of the telescope, during the past twenty-five years.

Yvette Cendes, a graduate student with the University of Toronto and the Leiden Observatory, has created a time-lapse showing the aftermath of the supernova over a 25-year period, from 1992 to 2017. The images show the shockwave expanding outward and slamming into debris that ringed the original star before its demise.

In an accompanying paper, published in the Astrophysical Journal on October 31st, Cendes and her colleagues add to the evidence that the expanding remnant is shaped—not like a ring like those of Saturn’s—but like a donut, a form known as a torus. They also confirm that the shockwave has now picked up some one thousand kilometres per second in speed. The acceleration has occurred because the expanding torus has punched through the ring of debris.

The animation, which I have embedded below the fold, uses images produced by an array radio telescopes in Australia.
» Read more

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Hawaii Supreme Court rules in favor of TMT

9:04 am

Hawaii’s Supreme Court today upheld by a 4-1 vote the construction permits of the consortium building the Thirty Meter Telescope (TMT) on Mauna Kea.

In its own press release, the TMT consortium said that it “will move forward with fulfilling the numerous conditions and requirements of [the state’s permit] prior to the start of any construction.”

The comments by one of the the telescope’s opponents at the first link are revealing.

Kealoha Pisciotta, one of the main leaders against the telescope, said she’s doesn’t know what their next steps will be, but she’s not hopeful that more legal wrangling will help. “The court is the last bastion in democracy,” she said. “The only other option is to take to the streets. If we lose the integrity of the court, then you’re losing normal law and order, and the only other option is people have to rise up.” [emphasis mine]

Let me translate: We didn’t get our way, so we’re now going to throw another tantrum! Expect more protests and attempts to block construction. Expect the Hawaiian government, dominated almost entirely by Democrats, to fold to those protests. Expect more delays. For example, do you really think the permit process was really done?

State Department of Land and Natural Resources Chairwoman Suzanne Case said the next steps involve telescope builders submitting construction plans. The department will review the plans before issuing permission to proceed.

This was all done almost a decade earlier, and was exactly what the Supreme Court ruled on. To bring it up now suggests the state government is still quietly looking for loopholes to stop the construction, even though the public supports construction and the protesters are a decided minority.

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NASA officially retires Kepler

12:42 pm

NASA today officially retired Kepler after nine years of operations.

After nine years in deep space collecting data that indicate our sky to be filled with billions of hidden planets – more planets even than stars – NASA’s Kepler space telescope has run out of fuel needed for further science operations. NASA has decided to retire the spacecraft within its current, safe orbit, away from Earth. Kepler leaves a legacy of more than 2,600 planet discoveries from outside our solar system, many of which could be promising places for life.

Exoplanet hunting however does not end here. Unlike Hubble, astronomers and NASA planned ahead for Kepler’s demise, and this year launched TESS to continue its work, in an even more sophisticated manner.

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Fast radio bursts not detected at certain radio wavelengths

8:47 am

In observations by two different radio telescopes operating at different radio wavelengths but looking at the same part of the sky, astronomers have found that an observed fast radio burst was not detected by one of those telescopes.

The Curtin University-led Murchison Widefield Array (MWA) and CSIRO’s Australian SKA Pathfinder (ASKAP) telescopes were searching the sky for fast radio bursts, which are exceptionally bright flashes of energy coming from deep space. These extreme events last for only a millisecond but are so bright that many astronomers initially dismissed the first recorded fast radio burst as an observational error.

In research published in the Astrophysical Journal Letters, astronomers describe how ASKAP detected several extremely bright fast radio bursts, but the MWA—which scans the sky at lower frequencies—did not see anything, even though it was pointed at the same area of sky at the same time.

Lead author Dr Marcin Sokolowski, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said the fact that the fast radio bursts were not observed at lower frequencies was highly significant. “When ASKAP sees these extremely bright events and the MWA doesn’t, that tells us something really unexpected is going on; either fast radio burst sources don’t emit at low frequencies, or the signals are blocked on their way to Earth,” Dr Sokolowski said.

If blocked at these lower frequencies, this tells theorists something about the environment where the burst occurred. If instead the burst does not emit in those lower frequencies, it tells them something about the burst itself.

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Number of candidate exo-Earths reduced by Gaia data

8:32 am

Worlds without end: The number of candidate exo-Earths identified by Kepler has now been reduced based on data from Europe’s Gaia telescope.

To date, NASA’s prolific Kepler space telescope has discovered about 30 roughly Earth-size exoplanets in their host stars’ “habitable zone” — the range of orbital distances at which liquid water can likely exist on a world’s surface.

Or so researchers had thought. New observations by the European Space Agency’s (ESA) Gaia spacecraft suggest that the actual number is probably significantly smaller — perhaps between two and 12, NASA officials said today.

Gaia launched in December of 2013 to create an ultraprecise 3D map of the Milky Way. So far, this map includes position information for about 1.7 billion stars and distance data for about 1.3 billion stars, according to NASA officials. Gaia’s observations suggest that some of the Kepler host stars are brighter and bigger than previously believed, the officials added. Planets orbiting such stars are therefore likely larger and hotter than previously thought.

Being hotter and larger, the habitable zone for these stars shifts outward, placing the exoEarth’s outside the habitable zone.

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Hubble resumes science operations

8:27 am

After three weeks of successful trouble-shooting of a backup gyroscope scientists have now returned the Hubble Space Telescope to full science operations.

Everyone should understand that this situation is now very temporary. Hubble no longer has any backup gyroscopes. If another fails, they will have to go to a one-gyroscope mode, holding the second working gyroscope back as a back-up, in order to extend the telescope’s life as much as possilbe. In that mode the telescope can operate for a significant period, but will have limited capabilities.

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