Tag: astronomy

The cameras that saved Hubble

11:42 pm

Link here. It is the 25th anniversary this week of the space shuttle mission that installed the two cameras that fixed the mirror issue on the Hubble Space Telescope, and the press release at the link provides a nice short overview of that mission, and what was involved to make it happen.

Of course, for a much more detailed look at this story, you could also buy and read A Universe in a Mirror. There are a lot of very fascinating stories that no single press release can possibly mention that I described with glee in writing this book.

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Four more gravitational wave detections

9:16 am

The uncertainty of science: The scientists running the LIGO gravitational wave detector have announced the detection of four more gravitational waves, bringing to eleven the total number so far observed.

During the first observing run O1, from September 12, 2015 to January 19, 2016, gravitational waves from three BBH mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded a binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational wave events being reported now. The new events are known as GW170729, GW170809, GW170818 and GW170823 based on the dates on which they were detected. With the detection of four additional BBH mergers the scientists learn more about the population of these binary systems in the universe and about the event rate for these types of coalescences.

The observed BBHs span a wide range of component masses, from 7.6 to 50.6 solar masses. The new event GW170729 is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

In two BBHs (GW151226 and GW170729) it is very likely that at least one of the merging black holes is spinning. One of the new events, GW170818, detected by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. It is the best localized BBH to date: its position has been identified with a precision of 39 square degrees (195 times the apparent size of the full moon) in the northern celestial hemisphere. [emphasis mine]

The highlighted quote above illustrates the amount of uncertainty here. Though these appear to be gravitational waves, and have been confirmed in multiple ways, the data is very coarse, providing only a limited amount of basic information about each event. This limited information is still very valuable, and certainly advances our understanding of black holes and their formation, but it is important to recognize the limitations of that data.

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Astronomers get best and earliest view of supernovae ever

9:15 am

Using ground-based telescopes as well as the space telescope Kepler astronomers have obtained their best and earliest view of a Type Ia supernova.

The supernova, named SN 2018oh, was brighter than expected over the first few days. The increased brightness is an indication that it slammed into a nearby companion star. This adds to the growing body of evidence that some, but not all, of these thermonuclear supernovae have a large companion star that triggers the explosion.

Las Cumbres Observatory (LCO), based in Goleta, California, is a global network of 21 robotic telescopes that obtained some of the best data characterizing the supernova in support of the NASA mission. Wenxiong Li, the lead author of one of three papers published today on the finding, was based at LCO when much of the research was underway. Five other LCO astronomers, who are affiliated with the University of California Santa Barbara (UCSB), also contributed to two of the papers.

Understanding the origins of Type Ia supernovae is critical because they are used as standard candles to map out distances in cosmology. They were used to discover Dark Energy, the mysterious force causing the universe to accelerate in its expansion. Astronomers have long known that a supernova is the explosion of a dense white dwarf star (A white dwarf has the mass of the sun, but only the radius of the Earth; one teaspoon of a white dwarf would weigh roughly 23000 pounds) What triggers the explosion is less well understood. One theory holds that the explosions are the merger of two white dwarf stars. Another is that the second star is not a white dwarf at all, but a normal-sized or even giant star that loses only some of its matter to the white dwarf to initiate the explosion. In this theory, the explosion then smashes into the surviving second star, causing the supernova to be exceedingly bright in its early hours.

Finding that Type Ia supernovae can be brighter than previously believed throws a wrench into the results that discovered dark energy, since those results made assumptions about the brightness and thus the distance of those supernovae. If the brightness of these supernovae are not as reliable as expected, they are also less of a standard candle for estimating distance.

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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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