From Science Alert: “Voyager Mission Reveals Unexpected Pressure at The Edge of The Solar System”

From Science Alert

10 OCT 2019
MIKE MCRAE

NASA astronomers have used data from the Voyager probes to measure the bustle of particles rippling at the very edge of our Solar System, and discovered the pressure in the distant borderlands of our star is higher than they expected.

The results suggest “that there are some other parts to the pressure that aren’t being considered right now that could contribute,” says Princeton University astrophysicist Jamie Rankin.

An illustration depicting the layers of the heliosphere. Credits: NASA/IBEX/Adler Planetarium

Maybe there are entire populations of particles out there that haven’t been taken into account yet. Or maybe it’s just a little hotter than anybody figured. The researchers have a number of possible explanations to explore in future research.

While the discovery itself is interesting enough, it’s the way they found it that makes for a truly fascinating bit of science.

As plasma in the shape of solar wind emanates from our Sun, it forms a ‘bubble’ we call the heliosphere. Fourteen billion kilometres away from the star, that wind effectively runs out of steam, as charged particles rapidly slow to subsonic speeds.

The edge of this bubble, called the heliosheath, is a zone where the density of those charged particles drops off and magnetic fields grow weak.

Beyond this messy border is a thin shell called the heliopause, where the haze of plasma blown out by the Sun trickles away, nudged by the subtle influence of our galactic neighbours as our star moves through space.

At this ‘pause’, the pressure of local interstellar space pushing in and the heliosheath pushing out must balance out. Knowing exactly what this looks like, though, is no easy task. We can make models to estimate, but nothing beats hard evidence.

Fortunately, we happen to have two probes passing through that part of the Solar System. Take a look at NASA’s handy diagram below to see how it all fits together.

The Voyager spacecraft, one in the heliosheath and the other just beyond in interstellar space, took measurements as a solar even known as a global merged interaction region passed by each spacecraft four months apart. These measurements allowed scientists to calculate the total pressure in the heliosheath, as well as the speed of sound in the region. Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith

Voyager 1 is about 20 billion kilometres away, effectively out in the wild emptiness we think of as interstellar space. Its partner, Voyager 2, isn’t far behind, right on the cusp of making an exit.

NASA/Voyager 1

NASA/Voyager 2

Neither has a direct way of telling us much about the pressures of space in that area, but a recent flare-up in solar activity called a global merged interaction region (GMIR) provided a prime opportunity to work it out.

“There was really unique timing for this event because we saw it right after Voyager 1 crossed into the local interstellar space,” says Rankin.

“And while this is the first event that Voyager saw, there are more in the data that we can continue to look at to see how things in the heliosheath and interstellar space are changing over time.”

The solar activity was effectively a shout into space, sending a pulse of particles roaring out into the distance. This cry rippled into the heliosheath in 2012, where Voyager 2 was watching and listening. Roughly three months later, Voyager 1 also felt its effects.

From each set of observations, the researchers calculated the pressure at the boundary to be around 267 femtopascals, which is an absolutely minuscule fraction of the kind of atmospheric pressure we experience here on Earth.

It might be a relatively tiny squeeze, but the researchers were surprised.

“In adding up the pieces known from previous studies, we found our new value is still larger than what’s been measured so far,” says Rankin.

The team were also able to calculate the speed of sound waves passing through this medium – a speedy 314 kilometres per second. Or a thousand times faster than sound travelling through our own atmosphere.

There was one other surprise to come. The wave’s passage lined up with an apparent drop in the intensity of high speed particles called cosmic rays. The fact each of the probes experienced this same thing in two different ways gives astrophysicists yet another mystery to solve.

“Trying to understand why the change in the cosmic rays is different inside and outside of the heliosheath remains an open question,” says Rankin.

The Voyager probes might be getting a little old, but given how busy it looks out on the edge of the Solar System, we’re glad they haven’t fully retired yet.

This research was published in The Astrophysical Journal.

See the full article here .

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From Science Alert: “Astronomers Detect a ‘Hot Jupiter’ With a Staggering 18-Hour-Short Orbit”

From Science Alert

1 OCT 2019
MICHELLE STARR

We have a new record. Perhaps 1,060 light-years away, a gas giant called NGTS-10b is whipping around its star so closely, it completes an entire orbit in just 18.4 hours.

Artist’s impression of a transiting gas giant. (NASA, ESA and G. Bacon)

That’s nearly as close as the planet can get to the host star without being ripped apart by gravitational forces. But it will get closer.

Astronomers have estimated that the exoplanet is spiralling in towards the star, and will cross that ripping-apart point – called the Roche limit – in just 38 million years. It’s utterly doomed.

The finding makes this solar system an incredible laboratory for studying tidal interactions between a star and a perilously close giant exoplanet. A paper describing the exoplanet – which belongs to the ‘hot Jupiter’ type – has been published on pre-print resource arXiv [submitted to MNRAS].

Hot Jupiters are fascinating exoplanets. As the name suggests, they are gas giants like Jupiter; unlike Jupiter, however, they orbit very closely to their host stars, with orbital periods of less than 10 days. This is what makes them “hot” (and here you were thinking it was the swimsuits).

According to current models of planet formation, technically hot Jupiters shouldn’t exist. A gas giant can’t form that close to their star, because the gravity, radiation, and intense stellar winds ought to keep the gas from clumping together.

However, they do exist; of the over 4,000 confirmed exoplanets discovered to date, up to 337 could be hot Jupiters. It’s thought that they form farther out in their planetary systems, then migrate inwards towards the star.

We may not know much about their mysterious births, but hot Jupiters that are particularly close to their stars can tell us a lot about star-planet tidal interactions. Hence, they are among the most studied exoplanets in the galaxy.

Until this latest breakneck discovery, only six of these enigmatic gas giants had ever been detected with an orbital period of less than one day – WASP-18b (22.6 hours), WASP-19b (18.9 hours), WASP-43b (19.5 hours), WASP-103b (22.2 hours), HATS-18b (20.1 hours) and KELT-16b (23.3 hours).

NGTS-10b, discovered using the ground-based Next-Generation Transit Survey in Paranal, Chile, marks the seventh of these ultra-close hot Jupiters, and it has the shortest orbital period of them all.

ESO NGTS an array of twelve 20-centimetre telescopes at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

Between 21 September 2015 and 14 May 2016, a single telescope observed the star now known as NGTS-10 over 237 nights. The survey wasn’t officially operational yet, but it captured 220,918 10-second exposures of the star during this commissioning phase.

It seemed like a relatively unremarkable main sequence star – around 10 billion years old K-type orange star, just under 70 percent of the Sun’s size and mass.

But a closer look at those images revealed that the star was dimming slightly every 18.4 hours. So an international team of astronomers led by James McCormac of the University of Warwick set to work, using that data and additional observations to characterise the exoplanet responsible for the dimming.

They determined that NGTS-10b is just over 1.2 times the size of Jupiter, and just over 2.1 times its mass. And it’s orbiting the star at 1.46 times the Roche radius – meaning it’s right on the verge (in cosmic time) of tidal devastation.

At such proximity to the star, even though it’s not yet close enough to pull NGTS-10b apart, the exoplanet will be flattened at the poles as the star’s gravity pulls it out of shape, an oblate spheroid rather than a nice, plump round sphere.

The team was careful to rule out a binary companion of the host star as a cause of the dimming. So, we are as sure as we can be that the exoplanet exists. The problem is that the light from the neighbouring stars has made it somewhat difficult to calculate an accurate distance to NGTS-10.

The 1,060 light-year distance was calculated based on Gaia data, the most accurate three-dimensional map of the Milky Way galaxy to date, but there’s still a margin for error. If the distance is incorrect, that may mean some of the size and mass data is slightly incorrect, too.

That issue can be resolved by studying the next release of Gaia data, due to drop in batches in 2020 and 2021.

Meanwhile, continued observations of the system could reveal the exoplanet’s orbital decay. The team predicts that the orbit will shorten by 7 seconds over the next 10 years. If astronomers can obtain precise enough measurements of the system, they may be able to see it happening.

See the full article here .

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From Science Alert: “Faster-Than-Light Speeds Could Be Why Gamma-Ray Bursts Seem to Go Backwards in Time”

From Science Alert

30 SEP 2019
MICHELLE STARR

Artist’s impression of a relativistic jet. (DESY, Science Communication Lab)

Time, as far as we know, moves only in one direction. But last year, researchers found events in some gamma-ray burst pulses that seemed to repeat themselves as though they were going backwards in time.

Now, new research suggests a potential answer for what might be causing this time reversibility effect. If waves within the relativistic jets that produce gamma-ray bursts travel faster than light – at ‘superluminal’ speeds – one of the effects could be time reversibility.

Such speeding waves could actually be possible. We know that when light is travelling through a medium (such as gas or plasma), its phase velocity is slightly slower than c – the speed of light in a vacuum, and, as far as we know, the ultimate speed limit of the Universe.

Therefore, a wave could travel through a gamma-ray burst jet at superluminal speeds without breaking relativity. But to understand this, we need to back up a little to look at the source of those jets.

Gamma-ray bursts are the most energetic explosions in the Universe. They can last from a few milliseconds to several hours [The Astrophysical Journal], they’re extraordinarily bright, and we don’t yet have a comprehensive list of what causes them.

We know from the 2017 observations [Physical Review Letters] of colliding neutron stars that these smash-ups can create gamma-ray bursts. Astronomers also think such bursts are produced when a massive, rapidly spinning star collapses into a black hole, violently ejecting material into the surrounding space in a colossal hypernova.

That black hole is then surrounded by a cloud of accretion material around its equator; if it’s rotating quickly enough, the fallback of the initially exploded material will result in relativistic jets shooting from the polar regions, blasting through the outer envelope of the progenitor star before producing gamma-ray bursts.

Now, back to those waves travelling faster than light.

We know that, when travelling through a medium, particles can move faster than light does. This phenomenon is responsible for the famous Čerenkov radiation, often seen as a distinctive blue glow.

Čerenkov radiation

That glow – a ‘luminal boom’ – is produced when charged particles such as electrons move faster through water than the phase velocity of light.

Astrophysicists Jon Hakkila of the College of Charleston and Robert Nemiroff of the Michigan Technological University believe that this same effect can be observed in gamma-ray burst jets, and have conducted mathematical modelling to demonstrate how.

“In this model an impactor wave in an expanding gamma-ray burst jet accelerates from subluminal to superluminal velocities, or decelerates from superluminal to subluminal velocities,” they write in their paper [The Astrophysical Journal].

“The impactor wave interacts with the surrounding medium to produce Čerenkov and/or other collisional radiation when travelling faster than the speed of light in this medium, and other mechanisms (such as thermalised Compton or synchrotron shock radiation) when travelling slower than the speed of light.

“These transitions create both a time-forward and a time-reversed set of [gamma-ray burst] light curve features through the process of relativistic image doubling.”

Such relativistic image doubling is thought to occur in Čerenkov detectors. When a charged particle travelling at near light-speed enters water, it moves faster than the Čerenkov radiation it produces, and therefore can hypothetically appear to be in two places at once: one image appearing to move forward in time and the other appearing to move backwards.

Mind you, this doubling has not yet been experimentally observed. But if it does occur, it could also be responsible for producing the time-reversibility seen in gamma-ray burst light curves, occurring both when the impactor wave travelling through the jet medium accelerates to speeds faster than light, and decelerates to subluminal speeds.

More work is needed, of course. The researchers assumed that the impactor responsible for creating a gamma-ray burst would be a large-scale wave produced by changes in, say, density, or the magnetic field. That will need further analysis. And if the plasmas involved aren’t transparent to superluminal radiation, all bets are off.

However, the researchers said, their model provides better explanations for the characteristics of gamma-ray burst light curves than models that don’t include time reversibility.

“Standard gamma-ray burst models have neglected time-reversible light curve properties,” Hakkila said. “Superluminal jet motion accounts for these properties while retaining a great many standard model features.”

See the full article here .

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From Science Alert: “Astronomers Catch The Immediate Aftermath of a Black Hole Destroying a Star”

From Science Alert

27 SEP 2019
MICHELLE STARR

Illustration of a supermassive black hole disrupting a star. (NASA/JPL-Caltech)

For all our perception of supermassive black holes as gravitational vortices ravenously devouring stars, it doesn’t actually happen that often. For instance, our galaxy’s own black hole might only do it a handful of times every 100,000 years.

So it’s quite a special occasion for the astronomers who have just observed the immediate aftermath of this devouring event. In fact, this new observation is the earliest we’ve ever seen it happen.

This means we could observe it with multiple telescopes. In turn, those observations have delivered a tremendous wealth of data that can help to refine our understanding of how supermassive black holes gobble up stars – what are known as tidal disruption events (TDEs).

This particular TDE occurred around a supermassive black hole 6.3 million times the mass of the Sun (our own Milky Way’s Sagittarius A* is 4 million solar masses), in a galaxy called 2MASX J07001137-6602251, roughly 375 million light-years away.

(Standard disclaimer – what we’re seeing actually happened 375 million years ago, but the light is only reaching us now, so we refer to the events as occurring when we experienced them.)

And it just so happened that this TDE occurred in the tiny patch of sky being continuously watched by NASA’s planet-hunting telescope TESS.

NASA/MIT TESS replaced Kepler in search for exoplanets

In turn, TESS is being monitored by the All-Sky Automated Survey for Supernovae (ASAS-SN).

ASAS-SN’s hardware. Off the shelf Mark Elphick-Los Cumbres Observatory

When TESS noticed something in the sky growing brighter, astronomers were alerted straight away, and sprung into action to turn a number of telescopes towards 2MASX J07001137-6602251.

Sure enough, the supermassive black hole had caught a star, with intense gravity pulling the star apart. The team has not yet determined the mass of the victim, but the event was so energetic it produced a light peak over 10 orders of magnitude brighter than the Sun – and four times brighter than its host galaxy.

And, spectacularly, a team of astronomers got to watch that peak build from the earliest moment when we could have even detected the event.

“This is the earliest we’ve ever seen emission from a TDE, and the earliest we could possibly see it – because TESS was already monitoring the part of the sky where it happened, we got to see exactly when it started to get brighter,” astronomer Tom Holoien of Carnegie Science told Science Alert.

“There are only about 4 or 5 TDEs that are published that have been found prior to peak at all, and none were as early as this.”

The event – named ASASSN-19bt – was first detected by TESS on 29 January 2019. Because it seemed to come from the central region of the host galaxy, a closer look was warranted. On 31 January, the team studied the region using the Low-Dispersion Survey Spectrograph 3 (LDSS-3), mounted on the Magellan Clay telescope in Chile.

Low-Dispersion Survey Spectrograph 3 (LDSS-3), mounted on the Magellan Clay telescope in Chile

Las Campanas Clay Magellan telescope, located at Carnegie’s Las Campanas Observatory, Chile, approximately 100 kilometres (62 mi) northeast of the city of La Serena, over 2,500 m (8,200 ft) high

This revealed that the event was likely a TDE, and more observations were taken; the NASA Swift Observatory imaged the event in ultraviolet and X-rays; the ESA XMM-Newton took spectra; and ground-based telescopes at Las Cumbres Observatory [Clay Magellan telescope above] took optical images.

NASA Neil Gehrels Swift Observatory

ESA/XMM Newton

ASASSN-19bt reached peak brightness on 4 March 2019, and the team continued to observe the event months after (although their paper only covers until 10 April).

And there were some big surprises.

“NASA’s Swift satellite .. indicated that for the first few days after discovery the TDE actually got fainter and cooled down considerably. This has never been seen before – typically before it reaches its maximum brightness we would see the brightness rise steadily, and the temperature typically remains constant,” Holoien said

“In this case, we see both the brightness and temperature drop sharply before it follows the usual evolution that we’ve seen before. This also could be a common feature in TDEs, but we just don’t know, because no TDE has had Swift data this early.”

In addition, the host galaxy is younger and dustier than other galaxies in which such events have been observed. And, as the TDE brightened towards peak, the increase in luminosity was very smooth. This is something else that hadn’t been seen before.

At the very earliest part of the observations, the emissions are coming from extraordinarily close to the black hole, Holoien told ScienceAlert – maybe a few tens of times the size of the event horizon, as close to the black hole as Mars or Earth is to the Sun.

When you remember how far that galaxy is, that’s pretty extraordinary.

“I actually got chills when I saw the TESS light curve for the first time, because no TDE has been observed anywhere close to as early, or on as rapid a cadence,” he said. “When I saw it, I said we had to write this paper ASAP, because this was going to be an amazing dataset – and then we found the other interesting aspects too!”

The team continued to monitor ASASSN-19bt for three months following the peak, and will be publishing their results in a separate paper. It will mark the most complete and comprehensive dataset ever published for a tidal disruption event.

Meanwhile, fingers remain crossed that TESS will get this lucky again, so that scientists will have a separate dataset for comparison.

“These observations are so early that while they’re generally in-line with the physical models, none of the theory had exactly predicted what we see, so these observations will hopefully help us refine those models,” Holoien said.

The research has been published in The Astrophysical Journal.

See the full article here .

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From Science Alert: “The Biggest Volcano on Io May Be About to Erupt, And Scientists Are Watching Closely”

18 SEP 2019
MICHELLE STARR

Voyager 1 image of the Loki patera. (NASA/JPL/USGS)

NASA/Voyager 1

The biggest volcano on Jupiter’s moon Io could be about to blow. Decades of observation have revealed a periodic cycle in the volcano’s eruptions; according to past behaviour, it’s due for the next one any day.

That potential burst of activity – or lack thereof – could help us to better understand the volcano and Io itself, the most volcanically active object in the Solar System.

The massive volcano, called Loki, was originally discovered to have a cycle of around 540 days. This was based on years of observations between 1988 and 2000, described in a 2002 paper [Geophysical Research Letters] led by physicist and planetary scientist Julie Rathbun of the Planetary Science Institute.

At the start of the eruption, Loki would brighten, and remain bright for around 230 days before falling darker again. Then, the cycle would repeat. This was happening like clockwork until 2001, when the volcano stopped brightening and dimming.

Then, in 2013, Loki started up again, but on a slightly shorter cycle – 475 days, instead of 540. It’s been on a 475-day cycle ever since.

“If this behaviour remains the same, Loki should erupt in September 2019,” Rathbun said. “We correctly predicted that the last eruption would occur in May of 2018.”

Rathbun and her team interpreted Loki as a lake of lava in a crater-like depression called a patera about 200 kilometres (124 miles) across. As the cooling crust on the surface of the lake becomes gravitationally unstable and collapses into it, the pool “overturns”, flooded by fresh lava.

This was supported by observations reported in 2017 that saw waves of lava slowly rolling across the patera – a process that can take up to 230 days.

What caused the hiatus in this cycle between 2001 and 2013 is not yet known, but one possible explanation could implicate changes in the volatile content in the magma, which affects the density of both magma and crust. Even a small change can produce large variations in how long the crust takes to sink.

The last eruption started sometime between 23 May and 6 June 2018. That means the 475-day window is between 9 and 24 September. It may have already started.

“Volcanoes are so difficult to predict because they are so complicated. Many things influence volcanic eruptions, including the rate of magma supply, the composition of the magma – particularly the presence of bubbles in the magma, the type of rock the volcano sits in, the fracture state of the rock, and many other issues,” Rathbun said.

“We think that Loki could be predictable because it is so large. Because of its size, basic physics are likely to dominate when it erupts, so the small complications that affect smaller volcanoes are likely to not affect Loki as much.”

Rathbun presented her findings at the EPSC-DPS Joint Meeting 2019 in Geneva.

See the full article here .

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From University of Hawaii via Science Alert: “Black Holes May Hide Cores of Pure Dark Energy That Keep The Universe Expanding

From University of Hawaii

via

Science Alert

12 SEP 2019
MIKE MCRAE

(Just_Super/iStock)

A fifty-year-old hypothesis predicting the existence of bodies dubbed Generic Objects of Dark Energy (GEODEs) is getting a second look in light of a proposed correction to assumptions we use to model the way our Universe expands.

If this new version of a classic cosmological model is correct, some black holes could hide cores of pure dark energy, pushing our Universe apart at the seams.

University of Hawai’i astrophysicist Kevin Croker and mathematician Joel Weiner teamed up to challenge the broadly accepted notion that when it comes to the Universe’s growing waistline, its contents are largely irrelevant.

“For 80 years, we’ve generally operated under the assumption that the Universe, in broad strokes, was not affected by the particular details of any small region,” said Croker.

“It is now clear that general relativity can observably connect collapsed stars – regions the size of Honolulu – to the behaviour of the Universe as a whole, over a thousand billion billion times larger.”

Not only could this alternative interpretation of fundamental physics change how we understand the Universe’s expansion, but we might need to also consider how that growth might affect compact objects like the cores of collapsing stars.

The fact that space has been steadily adding real estate for the past 13.8 billion years is by now a widely accepted feature of our Universe.

The set of equations we use to describe this expansion was first put to paper just under a century ago by the Russian physicist Alexander Friedmann. They provided a solution to Einstein’s theory of general relativity that now underpins our big picture model of cosmology.

As useful as Friedmann’s equations have been, they’re based on the assumption that any matter floating around inside this expanding space is more or less made of the same kind of stuff, and spread out fairly evenly.

This means we tend to ignore the swirls of stars and galaxies – just like we might not include ducks in the hydrodynamics of a lake.

But Croker and Weiner wonder what might happen to space and the objects it contains if we made some reasonable changes to the assumptions that inform these equations.

The consequences aren’t trivial.

According to their adjusted model, the averaged contributions of our metaphorical ducks might affect the lake’s water after all.

What’s more, the lake’s expansion would also affect how the ducks swim, causing them to lose or gain energy depending on their species.

Theoretically, this interpretation would mean we need to take the Universe’s growth into account when describing certain phenomena, such as the death of a star.

In 1966, a Russian physicist named Erast Gliner considered how some densities of space close to the Big Bang might look – in terms of relativity – like a vacuum that could counter the effects of gravity.

His solution would look like a black hole from the outside. But inside would be a bubble of energy shoving against the surrounding Universe.

Half a century later, astrophysicists are on the hunt for just such a pushing power that might be responsible for the Universe’s expansion picking up speed over time.

Today we refer to this undescribed force as dark energy, but could Gliner’s pockets of relativistic nothingness be the source of our Universe’s accelerating expansion?

Based on Croker and Weiner’s work, if just a few ancient stars were to have collapsed into Gliner’s GEODEs instead of the more typical puckered space of a singularity, their average effect on expanding space would look just like dark energy.

The pair go further, applying their corrected model to the first observation of gravitational waves from a black hole collision as measured by LIGO.

To make the math fit, it’s assumed the stars that formed the merging black holes formed in a low-metallicity environment, which makes them somewhat rare.

Technically, the energy of a GEODE should evolve as the Universe grows, effectively compacting as a cosmological equivalent of a ‘blueshift’.

If the merging black holes were GEODEs, according to the researchers, there’d be no need to assume the black holes were born in an unusual patch of space.

“What we have shown is that if GEODEs do exist, then they can easily give rise to observed phenomena that presently lack convincing explanations,” the researchers said.

“We anticipate numerous other observational consequences of a GEODE scenario, including many ways to exclude it. We’ve barely begun to scratch the surface.”

Testing assumptions like these is a vital part of physics. We’re a long way off including GEODEs in any official astrophysical zoo of weird objects, but it’s possible these could be the dark hearts of the Universe we’ve been looking for.

This research was published in The Astrophysical Journal.

See the full article here .

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The University of Hawai‘i System includes 10 campuses and dozens of educational, training and research centers across the Hawaiian Islands. As the public system of higher education in Hawai‘i, UH offers opportunities as unique and diverse as our Island home.

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From Bar Ilon University and Riken via Science Alert: “Physicists Have Finally Built a Quantum X-Ray Device”

From Bar Ilon University

and

From RIKEN

via

Science Alert

2 SEP 2019
MICHELLE STARR

(APS/Alan Stonebraker)

A team of researchers has just demonstrated quantum enhancement in an actual X-ray machine, achieving the desirable goal of eliminating background noise for precision detection.

The relationships between photon pairs on quantum scales can be exploited to create sharper, higher-resolution images than classical optics. This emerging field is called quantum imaging, and it has some really impressive potential – particularly since, using optical light, it can be used to show objects that can’t usually be seen, like bones and organs.

Quantum correlation describes a number of different relationships between photon pairs. Entanglement is one of these, and is applied in optical quantum imaging.

But the technical challenges of generating entangled photons in X-ray wavelengths are considerably greater than for optical light, so in the building of their quantum X-ray, the team took a different approach.

They used a technique called quantum illumination to minimise background noise. Usually, this uses entangled photons, but weaker correlations work, too. Using a process called parametric down-conversion (PDC), the researchers split a high-energy – or “pump” – photon into two lower-energy photons, called a signal photon and an idler photon.

“X-ray PDC has been demonstrated by several authors, and the application of the effect as a source for ghost imaging has been demonstrated recently,” the researchers write in their paper.

“However, in all previous publications, the photon statistics have not been measured. Essentially, to date, there is no experimental evidence that photons, which are generated by X-ray PDC, exhibit statistics of quantum states of radiation. Likewise, observations of the quantum enhanced measurement sensitivity have never been reported at X-ray wavelengths.”

The researchers achieved their X-ray PDC with a diamond crystal. The nonlinear structure of the crystal splits a beam of pump X-ray photons into signal and idler beams, each with half the energy of the pump beam.

Normally, this process is very inefficient using X-rays, so the team scaled up the power. Using the SPring-8 synchrotron in Japan, they shot a 22 KeV beam of X-rays at their crystal, which split into two beams, each carrying 11 KeV.

SPring-8 synchrotron

SPring-8 synchrotron, located in Hyōgo Prefecture, Japan

The signal beam is sent towards the object to be imaged – in the case of this research, a small piece of metal with three slits – with a detector on the other side. The idler beam is sent straight to a different detector. This is set up so that each beam hits its respective detector at the same place and at the same time.

“The perfect time-energy relationship we observed could only mean that the two photons were quantum correlated,” said physicist Sason Sofer of Bar-Ilan University in Israel.

For the next step, the researchers compared their detections. There were only around 100 correlated photons per point in the image, and around 10,000 more background photons. But the researchers could match each idler to a signal, so they could actually tell which photons in the image were from the beam, thus easily separating out the background noise.

They then compared these images to images taken using regular, non-correlated photons – and the correlated photons clearly produced a much sharper image.

It’s early days yet, but it’s definitely a step in the right direction for what could be a greatly exciting tool. Quantum X-ray imaging could have a number of uses outside the range of current X-ray technology.

One promise is that it could lower the amount of radiation required for X-ray imaging. This would mean that samples easily damaged by X-rays could be imaged, or samples that require low temperatures; less radiation would mean less heat. It could also enable physicists to X-ray atomic nuclei to see what’s inside.

Obviously, since these quantum X-rays require a hardcore particle accelerator, medical applications are currently off the table. The team has demonstrated that it can be done, but scaling down is going to be tricky.

Currently, determining whether the photons are entangled is the next step. That would require the photons’ arrival at the detectors to be measured within attosecond scales, which is beyond our current technology.

Still, this is a pretty amazing achievement.

“We have demonstrated the ability to utilise the strong time-energy correlations of photon pairs for quantum enhanced photodetection. The procedure we have presented possesses great potential for improving the performances of X-ray measurements,” the researchers write.

“We anticipate that this work will open the way for more quantum enhanced x-ray regime detection schemes, including the area of diffraction and spectroscopy.”

The research has been published in Physical Review X.

See the full article here .

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RIKEN is Japan’s largest comprehensive research institution renowned for high-quality research in a diverse range of scientific disciplines. Founded in 1917 as a private research foundation in Tokyo, RIKEN has grown rapidly in size and scope, today encompassing a network of world-class research centers and institutes across Japan.

From Curtin University and ICRAR via Science Alert: “Millions of High-Speed Black Holes Could Be Zooming Around The Milky Way”

From Curtin University

and

From International Centre for Radio Astronomy Research

via

Science Alert

30 AUG 2019
MICHELLE STARR

(StudioM1/iStock)

How are black holes born? Astrophysicists have theories, but we don’t actually know for certain. It could be massive stars quietly imploding with a floompf, or perhaps black holes are born in the explosions of colossal supernovas. New observations now indicate it might indeed be the latter.

In fact, the research suggests that those explosions are so powerful, they can kick the black holes across the galaxy at speeds greater than 70 kilometres per second (43 miles per second).

“This work basically talks about the first observational evidence that you can actually see black holes moving with high velocities in the galaxy and associate it to the kick the black hole system received at birth,” astronomer Pikky Atri of Curtin University and the International Centre for Radio Astronomy Research (ICRAR) told ScienceAlert.

And it means there are potentially millions stellar-mass black holes zooming around the galaxy at high speed. The paper has been accepted into the Monthly Notices of the Royal Astronomical Society.

The study was based on 16 black holes in binary systems. Unless they’re actively feeding, we can’t actually find black holes, since no detectable electromagnetic radiation can escape their insane gravity. But if they’re in a binary pair and actively feeding on the other star, the matter swirling around the black hole gives off powerful X-rays and radio waves.

Once we can see these black hole beacons, we can see how the black hole is behaving. The international team of researchers used this behaviour to try and reconstruct the black hole’s history.

“We tracked how these systems were moving in our galaxy – so, figured out their velocities today, moved back in time, and tried to understand what the velocity was of the system when it was born, individually for each of these 16 systems,” Atri explained.

“Based on the velocities, you can actually find out if they were born with a supernova explosion, or if the stars just directly collapsed onto themselves without a supernova explosion.”

We know that neutron stars can be violently punted out across space at high speeds by their own supernova explosions – this is called a Blaauw kick, or natal kick, and it happens when the supernova explosion is lopsided, resulting in a recoil.

It was unknown if black holes could be kicked in the same way. Hypothetically, they might – and indeed seven black hole x-ray binaries have been previously associated with natal kicks.

The new research has analysed these, as well as nine others, in greater detail, combining measured proper motions, systemic radial velocities, and distances to these systems for the most detailed analysis yet.

The motion of one of these black holes as calculated by the team can be seen in the video below.

The researchers found that 12 of these 16 black hole X-ray binaries did indeed have high velocities and trajectories that indicated a natal kick. That’s 75 percent of the sample. If this scales up to the estimated 10 million black holes in the Milky Way, that might mean around 7.5 million high-speed black holes careening out there. And 10 million is a low estimate.

In line with previous theories, these speeding black holes are slower than kicked neutron stars by a factor of about three or four, due to their higher mass. Interestingly, there seemed to be no correlation between black hole mass and velocity, which means we don’t yet know if there’s a correlation between progenitor star mass and the likelihood of a supernova.

This is a relatively small sample size of black holes, of course. But, according to Atri, it’s a step towards building up a larger sample that can help us to understand how stars evolve and die, and give rise to black holes.

“Eventually, all of this will feed into how many black holes we expect in our galaxy, how many black holes that will actually merge to give those gravitational wave detections that LIGO finds,” she added.

To continue to build on the research, the team will keep watching the sky. These binary systems aren’t always bright – they come and go, transient. So the researchers are hoping to find more of these binary systems to continue building a census of Milky Way black holes, whether speeding or not.

And, in case you’re worried right now abut a black hole cruising right into our Solar System, you don’t really need to panic.

“The closest black hole, we think it’s two kiloparsecs away [6,523 light-years],” Atri said.

“It’s very, very far away. So there’s no chance that we’re getting sucked up by any black hole any time soon.”

See the full article here .

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ICRAR is an equal joint venture between Curtin University and The University of Western Australia with funding support from the State Government of Western Australia. The Centre’s headquarters are located at UWA, with research nodes at both UWA and the Curtin Institute for Radio Astronomy (CIRA).
ICRAR has strong support from the government of Australia and is working closely with industry and the astronomy community, including CSIRO and the Australian Telescope National Facility, <a
ICRAR is:

Playing a key role in the international Square Kilometre Array (SKA) project, the world's biggest ground-based telescope array.

Attracting some of the world’s leading researchers in radio astronomy, who will also contribute to national and international scientific and technical programs for SKA and ASKAP.
Creating a collaborative environment for scientists and engineers to engage and work with industry to produce studies, prototypes and systems linked to the overall scientific success of the SKA, MWA and ASKAP.

Murchison Widefield Array,SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO)

A Small part of the Murchison Widefield Array

Curtin University (formerly known as Curtin University of Technology and Western Australian Institute of Technology) is an Australian public research university based in Bentley and Perth, Western Australia. The university is named after the 14th Prime Minister of Australia, John Curtin, and is the largest university in Western Australia, with over 58,000 students (as of 2016).

Curtin was conferred university status after legislation was passed by the Parliament of Western Australia in 1986. Since then, the university has been expanding its presence and has campuses in Singapore, Malaysia, Dubai and Mauritius. It has ties with 90 exchange universities in 20 countries. The University comprises five main faculties with over 95 specialists centres. The University formerly had a Sydney campus between 2005 & 2016. On 17 September 2015, Curtin University Council made a decision to close its Sydney campus by early 2017.

Curtin University is a member of Australian Technology Network (ATN), and is active in research in a range of academic and practical fields, including Resources and Energy (e.g., petroleum gas), Information and Communication, Health, Ageing and Well-being (Public Health), Communities and Changing Environments, Growth and Prosperity and Creative Writing.

It is the only Western Australian university to produce a PhD recipient of the AINSE gold medal, which is the highest recognition for PhD-level research excellence in Australia and New Zealand.

Curtin has become active in research and partnerships overseas, particularly in mainland China. It is involved in a number of business, management, and research projects, particularly in supercomputing, where the university participates in a tri-continental array with nodes in Perth, Beijing, and Edinburgh. Western Australia has become an important exporter of minerals, petroleum and natural gas. The Chinese Premier Wen Jiabao visited the Woodside-funded hydrocarbon research facility during his visit to Australia in 2005.

From Science Alert and LIGO: “Scientists Detected 2 Black Hole Mergers Just 21 Mins Apart, But It’s Not What We Hoped”

From Science Alert

MIT /Caltech Advanced aLigo

31 AUG 2019
MIKE MCRAE

(Des Green/iStock)

Last Wednesday, a gravitational wave detection gave astronomers quite the surprise. As researchers were going about their work at the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of gravitational waves rolled in just minutes apart.

Gravitational waves. Credit: MPI for Gravitational Physics/Werner Benger

Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2018

Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

VIRGO Gravitational Wave interferometer, near Pisa, Italy

The first, labelled S190828j, was picked up by all three of LIGO’s gravitational wave detectors at 06:34 am, coordinated universal time.

MIT /Caltech Advanced aLigo

VIRGO Gravitational Wave interferometer, near Pisa, Italy

The second, S190828l, was measured at 06:55 – a mere 21 minutes later.

Both seemed to be the run-of-the-mill dying screams of black holes as they squish together. But here’s why it’s so surprising: astronomers wouldn’t expect to see a pair of signals in such quick succession.

In fact, this is only the second time two detections have rolled in on the same day. What’s more, at first glance they also seemed to echo from more or less the same patch of sky.

“This is a genuine “Uh, wait, what?; We’ve never seen that before…” moment in gravitational wave astronomy,” astrophysicist Robert Routledge from McGill University later tweeted, after openly speculating that it mightn’t be a mere coincidence.

Non-scientists — this is a genuine “Uh, wait, what? We’ve never seen that before…….” moment in gravitational wave astronomy. If you’d like to see how double-checks and confirmations and conclusions occur – pay attention, in real time. Happening now.
— Robert Rutledge (@rerutled) August 28, 2019

Nobody can blame Routledge for getting excited. Unexpected events like this are what discoveries are made of, after all. As he said, this is science in real time.

One possibility briefly kicked around was that S190828j and S190828l were actually the same wave, divided by some sort of distortion in space before being roughly thrown together again. This would have been huge.

Gravitational lensing – the warping effect an intervening mass has on space, as described by general relativity – can divide and duplicate the rays of light from far-off objects. It has become a useful tool for astronomers in the measurement of distances.

Gravitational Lensing NASA/ESA

If this had indeed been a two-for-one deal, it would be the first time a gravitational wave had been observed through a gravitational lens.

Alas, it’s now looking pretty unlikely. As the hours passed, new details emerged indicating the two signals don’t overlap enough to be originating from the same source.

If this were a lensing event, you’d expect the two localizations to sit more or less right on top of each other. They have similar shapes and appear in the same part of the sky, but they don’t really overlap: pic.twitter.com/lqvigNhyBl
— Robert McNees (@mcnees) August 28, 2019

So close, and yet so far. Right now, this twin event is looking more like a coincidence.

To look on the bright side, we now live in an age where the detection of the crash-boom of galactic giants isn’t a rare event, but rather an endless peel of thunder we can record and measure with an insane level of accuracy. It’s hard to believe the first collision was detected only a few years ago.

Scientists face a problem in the wake of freaky events like this one. On the one hand, wild speculations have a habit of taking on a life of their own when discussed so frankly in a public space, transforming into an established fact while barely half baked.

But time can be of the essence when we’re scanning a near-infinite amount of sky for clues, too. By throwing ideas out broadly, different groups of researchers can turn their attention to a phenomenon and collect data while it’s still hot.

This is what scientists do best – stumble across odd events, throw out ideas, and debate which ones deserve to be inspected and which should be abandoned.

If there’s more to S190828j and S190828l than meets the eye, we’ll let you know. For now, we can be disappointed that there was no Earth-shaking discovery, while still being amazed that we have the technology to discover it at all.

We really ought to celebrate the ‘disappointments’ a little more often.

See the full article here .

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From Spaceflight Insider: “Second group of names approved for features on Pluto” and Defense of Pluto’s Status as a planet

From Spaceflight Insider

August 26th, 2019
Laurel Kornfeld

A composite of images collected by New Horizons’ instruments during the spacecraft’s July 2015 Pluto flyby, this annotated map shows the newly-approved names in yellow and the ones approved in 2017 in white. Image Credit: NASA/JHUAPL/SwRI/Ross Beyer

A second set of names for features on Pluto, already used informally by members of NASA’s New Horizons mission, has received formal approval by the International Astronomical Union (IAU), the organization that names celestial objects and their features.

Submitted by the New Horizons mission, these 14 names honor pioneering explorers on Earth, space missions, scientists and engineers who have studied Pluto and the Kuiper Belt, and underworld mythology. Like the first set of 14 names for various features on Pluto’s surface, which were approved in 2017, all of these came from a 2015 public naming campaign organized jointly by the New Horizons mission, the SETI Institute, and the IAU.

NASA/New Horizons spacecraft

That campaign, titled “Our Pluto,” established a list of themes for names to be assigned to features on Pluto, Charon, and the system’s four small moons in advance of the July 2015 Pluto flyby. Themes for surface features on Pluto included names for the underworld from various world mythologies; gods, goddesses, and dwarfs associated with the underworld; heroes and other explorers of the underworld; writers associated with Pluto and the Kuiper Belt; and scientists and engineers associated with Pluto and the Kuiper Belt.

Participants could vote for names from a list of nominations suggested by the organizers or nominate a name of their choosing under the established categories.

____________________________________________________

From Science Alert
NASA Administrator Says Pluto Is Still a Planet, And Things Are Getting Heated
26 AUG 2019
MICHELLE STARR

Pluto. The Hindu

NASA Administrator Says Pluto Is Still a Planet, And Things Are Getting Heated.

Saturday 24 August 2019 marked a vexing anniversary for planetary scientists. It was 13 years to the day that Pluto’s official definition changed – what was once numbered among the planets of the Solar System was now but a humble dwarf planet.

But not everyone agreed with the International Astronomical Union’s ruling – and now NASA Administrator Jim Bridenstine has added his voice to the chorus declaring support for Pluto’s membership in the Solar System Planet Club.

“Just so you know, in my view, Pluto is a planet,” he said during a tour of the Aerospace Engineering Sciences Building at the University of Colorado Boulder.

“You can write that the NASA Administrator declared Pluto a planet once again. I’m sticking by that, it’s the way I learnt it, and I’m committed to it.”

Now, this doesn’t officially change anything, and his reasoning is a little facile – having learnt something one way doesn’t mean it has to stay that way, thank you geocentrism. It’s an off-the-cuff lighthearted remark, and that’s fine.

But it just so happens that planetary scientists have been banging the Pluto planet drum for years, and their reasons are a little more considered. Actually, a lot more.

When the IAU removed Pluto from the list of what had been nine planets in the Solar System in August 2006, the move was a corollary of its official definitions of planets and dwarf planets.

Before that, there had been no official definitions of these objects, which created problems when astronomer Mike Brown of the California Institute of Technology and colleagues discovered an object that seemed to be bigger than Pluto. (This object was later designated a dwarf planet, and named Eris, after the Greek goddess of strife and discord.)

The difference between a planet and a dwarf planet that changed Pluto’s status? Pluto – hanging out as it does in the Kuiper Belt asteroid field – has not cleared “the neighbourhood around its orbit” of other rocks.

This helped to resolve the perceived problem of other objects around the same size of Pluto, of which there are potentially hundreds. If Pluto was in the planet club, what was keeping the rest of the riff-raff out?

Planetary scientist Alan Stern, leader of NASA’s New Horizon’s mission, has been vocal about his disappointment with the decision to de-planet Pluto since it was made.

“My conclusion is that the IAU definition is not only unworkable and unteachable, but so scientifically flawed and internally contradictory that it cannot be strongly defended against claims of scientific sloppiness, “ir-rigor,” and cogent classification,” he wrote in September 2006.

“The New Horizons project, like a growing number of the public, and many hundreds if not thousands of professional research astronomers and planetary scientists, will not recognise the IAU’s planet definition resolution of Aug. 24, 2006.”

And so he has not. In fact, earlier this year, he debated Ron Ekers of the IAU, defending Pluto’s planet status.

2:15:16

It’s not just that only 424 of around 9,000 IAU members voted on the resolution, nor that hundreds of planetary scientists immediately petitioned against it.

It’s also that Pluto has its own multilayered atmosphere, organic compounds, weather, moons.

It has landscapes – rocky mountain ranges and wide plains. It has avalanches, maybe plutoquakes, maybe even liquid oceans. And that the definition based on orbital clearing has no historical merit.

And even if it did, one could argue that other planets haven’t cleared their neighbourhoods either – there are a lot of asteroids hanging around both Earth and Jupiter’s orbits (although not nearly as many as the Kuiper Belt.)

Scientists last year argued that a planet should be defined as an object that has become large enough to become a sphere.

“It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body,” explained planetary physicist Philip Metzger of the University of Central Florida.

So far, the IAU has shown no signs of backing down, but neither do Pluto’s supporters. Perhaps Bridenstine joining Team Pluto will renew the fight. And we, for one, stand by to welcome our hundreds of new planetary pals.

See the full article here .

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SpaceFlight Insider reports on events taking place within the aerospace industry. With our team of writers and photographers, we provide an “insider’s” view of all aspects of space exploration efforts. We go so far as to take their questions directly to those officials within NASA and other space-related organizations. At SpaceFlight Insider, the “insider” is not anyone on our team, but our readers.

Our team has decades of experience covering the space program and we are focused on providing you with the absolute latest on all things space. SpaceFlight Insider is comprised of individuals located in the United States, Europe, South America and Canada. Most of them are volunteers, hard-working space enthusiasts who freely give their time to share the thrill of space exploration with the world.