Chemistry: Cosmic rays breed organics in space
Nature 535, 7611 (2016). doi:10.1038/535203b
Cosmic rays help to form the Universe's complex organic molecules — the building blocks of life on Earth.The interstellar gas clouds that give birth to stars and planets are rich in organic molecules, but scientists have struggled to explain how these formed. A team
Planetary science: Triple star hosts stable planet
Nature 535, 7611 (2016). doi:10.1038/535202a
An extrasolar planet in an exotic triple-star system lives in surprising harmony with the three suns hanging in its sky.Kevin Wagner of the University of Arizona in Tucson and his colleagues used the European Southern Observatory's Very Large Telescope in Chile to study the
Matter falling into a black hole heats up as it plunges to its doom. Before it passes into the black hole and is lost from view forever, it can reach millions of degrees. At that temperature it shines x-rays into space.
In the 1980s, astronomers discovered that the x-rays coming from black holes vary on a range of timescales and can even follow a repeating pattern with a dimming and re-brightening taking 10 seconds to complete. As the days, weeks and then months progress, the pattern’s period shortens until the oscillation takes place 10 times every second. Then it suddenly stops altogether.
This phenomenon was dubbed a Quasi Periodic Oscillation (QPO). During the 1990s, astronomers began to suspect that the QPO was associated with a gravitational effect predicted by Einstein’s general relativity which suggested that a spinning object will create a kind of gravitational vortex. The effect is similar to twisting a spoon in honey: anything embedded in the honey will be ‘dragged’ around by the twisting spoon. In reality, this means that anything orbiting around a spinning object will have its motion affected. If an object is orbiting at an angle, its orbit will ‘precess’ – in other words, the whole orbit will change orientation around the central object. The time for the orbit to return to its initial condition is known as a precession cycle.
In 2004, NASA launched Gravity Probe B to measure this so-called Lense-Thirring effect around Earth. By analysing the resulting data, scientists confirmed that the spacecraft would turn through a complete precession cycle once every 33 million years. Around a black hole, however, the effect would be much stronger because of the stronger gravitational field: the precession cycle would take just a matter of seconds to complete, close to the periods of the QPOs.
An international team of researchers, including Dr Matt Middleton from the Institute of Astronomy at the University of Cambridge, has used the European Space Agency’s XMM-Newton and NASA’s NuSTAR, both x-ray observatories, to study the effect of black hole H1743-322 on a surrounding flat disc of matter known as an ‘accretion disk’.
Close to a black hole, the accretion disc puffs up into a hot plasma, a state of matter in which electrons are stripped from their host atoms – the precession of this puffed up disc has been suspected to drive the QPO. This can also explain why the period changes - the place where the disc puffs up gets closer to the black hole over weeks and months, and, as it gets closer to the black hole, the faster its Lense-Thirring precession becomes.
The plasma releases high energy radiation that strikes the matter in the surrounding accretion disc, making the iron atoms in the disc shine like a fluorescent light tube. Instead of visible light, the iron releases X-rays of a single wavelength – referred to as ‘a line’. Because the accretion disc is rotating, the iron line has its wavelength distorted by the Doppler effect: line emission from the approaching side of the disc is squashed – blue shifted – and line emission from the receding disc material is stretched – red shifted. If the plasma really is precessing, it will sometimes shine on the approaching disc material and sometimes on the receding material, making the line wobble back and forth over the course of a precession cycle.
It is this ‘wobble’ that has been observed by the researchers.
“Just as general relativity predicts, we’ve seen the iron line wobble as the accretion disk orbits the black hole,” says Dr Middleton. “This is what we’d expect from matter moving in a strong gravitational field such as that produced by a black hole.”
This is the first time that the Lense-Thirring effect has been measured in a strong gravitational field. The technique will allow astronomers to map matter in the inner regions of accretion discs around back holes. It also hints at a powerful new tool with which to test general relativity. Einstein’s theory is largely untested in such strong gravitational fields. If astronomers can understand the physics of the matter that is flowing into the black hole, they can use it to test the predictions of general relativity as never before - but only if the movement of the matter in the accretion disc can be completely understood.
“We need to test Einstein’s general theory of relativity to breaking point,” adds Dr Adam Ingram, the lead author at the University of Amsterdam. “That’s the only way that we can tell whether it is correct or, as many physicists suspect, an approximation – albeit an extremely accurate one.”
Larger X-ray telescopes in the future could help in the search because they could collect the X-rays faster. This would allow astronomers to investigate the QPO phenomenon in more detail. But for now, astronomers can be content with having seen Einstein’s gravity at play around a black hole.
Adapted from a press release by the European Space Agency.
Image: ESA/ATG medialab.
An international team of astronomers has proved the existence of a ‘gravitational vortex’ around a black hole, solving a mystery that has eluded astronomers for more than 30 years. The discovery will allow astronomers to map the behaviour of matter very close to black holes. It could also open the door to future investigation of Albert Einstein’s general relativity.We need to test Einstein’s general theory of relativity to breaking pointAdam Ingram, University of AmsterdamESA/ATG medialabIllustration of gravitational vortex
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The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.
At the center of the Crab Nebula, located in the constellation Taurus, lies a celestial "beating heart" that is an example of extreme physics in space. The tiny object blasts out blistering pulses of radiation 30 times a second with unbelievable clock-like precision. Astronomers soon figured out that it was the crushed core of an exploded star, called a neutron star, which wildly spins like a blender on puree. The burned-out stellar core can do this without flying apart because it is 10 billion times stronger than steel. This incredible density means that the mass of 1.4 suns has been crushed into a solid ball of neutrons no bigger than the width of a large city. This Hubble image captures the region around the neutron star. It is unleashing copious amounts of energy that are pushing on the expanding cloud of debris from the supernova explosion like an animal rattling its cage. This includes wave-like tsunamis of charged particles embedded in deadly magnetic fields.
A team of astronomers led by the University of Arizona has directly imaged with the SPHERE instrument on ESO's Very Large Telescope the first planet ever found in a wide orbit inside a triple-star system. The orbit of such a planet had been expected to be unstable, probably resulting in the planet being quickly ejected from the system. But somehow this one survives. This observation of the HD 131399 system suggests that such systems may actually be more common than previously thought. The results will be published online in the journal Science on July 7, 2016. The artist's impression shows a view of the triple-star system HD 131399 from the giant planet orbiting the system. The planet is HD 131399Ab and appears at the lower left of the picture.
The result, published in the journal Nature, allows the mass of the Perseus Cluster – a swarm of thousands of galaxies that spans two million light years across and is one of the most massive known objects in the universe – to be calculated more accurately than before. Once this technique can be extended to other clusters, it will allow cosmologists to use them as better probes of our models of the Universe’s evolution from the Big Bang to the present time.
Hitomi (originally known as ASTRO-H) is the sixth in a series of Japanese x-ray observatories. Led by the Japan Aerospace Exploration Agency (JAXA), it is a collaboration of over 60 institutes and 200 scientists and engineers from Japan, the US, Canada, and Europe, including from the University of Cambridge. The spacecraft was launched on 17 February 2016 from the Tanegashima Space Center, Japan. However, JAXA announced in April that it was no longer possible to communicate with the satellite.
“Hitomi targeted the Perseus cluster just a week after it arrived in space,” said Matteo Guainazzi, the European Space Agency’s (ESA) Hitomi Resident Astronomer at the Institute of Space and Astronautical Science, Japan. “Perseus is the brightest x-ray galaxy cluster in the sky. It was therefore the best choice to fully demonstrate the power of the Soft X-ray Spectrometer (SXS), an x-ray micro-calorimeter that promised to deliver an unprecedented accuracy in the reconstruction of the energy of the incoming x-ray photons.” Waiting astronomers were not disappointed.
The Hitomi collaboration found that SXS could measure the turbulence in the cluster to a precision of 10 kilometres/second. But it was the absolute velocity of the gas that took them by surprise. It was just 164 ± 10 kilometres/second. The previous best measurement for Perseus was taken with ESA’s XMM-Newton x-ray observatory. Using a different type of spectrometer, it could only constrain the speed to be lower than 500 kilometres/second.
Hitomi’s measurement is therefore much more precise than any similar measurements performed in x-rays so far. “This is due to the outstanding performance and stability of the SXS in space. This demonstrates that the technology of x-ray micro-calorimeters can yield truly transformational results,” said Guainazzi.
The result indicates that the cluster gas has very little turbulent motions within. Turbulent motions in a fluid are part of our everyday life, as airplane passengers, swimmers, or parents filling a bathtub all experience. The study of such chaotic behaviour is also a powerful tool for astronomers to understand the behaviour of celestial objects.
Turbulent energy in Perseus is just four percent of the energy stored in the gas as heat. This is extraordinary considering that the active galaxy NGC 1275 sits at the heart of the cluster. It is pumping jetted energy into its surroundings, creating bubbles of extremely hot gas. It was thought that these bubbles induce turbulence, which keeps the central gas hot.
Hitomi shows that turbulent motion is almost absent from the cluster, and this gives rise to a mystery: what is keeping the cluster’s widespread gas hot?
“This result from Hitomi is telling us that in terms of how cluster cores work, we have to think very carefully about what is going on,” said the paper’s senior author Professor Andy Fabian of Cambridge’s Institute of Astronomy, and part of the Hitomi collaboration.
Fabian is working on the possibility of sound waves as the means of spreading the energy evenly throughout the gas. This is because in a sound wave, energy can be moved while the medium itself remains more or less stationary.
There are wider implications for this work too. Clusters of galaxies are the largest bound structures in the Universe. At the same time, they are also the smallest self-contained ‘boxes’. This means that matter is not flowing in or out of a cluster of galaxies. Instead, they each represent an island in which cosmic evolution has played out and been recorded.
Computer models of the expanding Universe use the distribution of cluster masses as an observational test of whether they are correct. Calculating the mass of a cluster depends upon the ratio of turbulent to quiescent gas. Any way of more accurately measuring turbulence allows better masses to be calculated, and therefore better computer models of the whole Universe to be developed.
Unfortunately, just a few weeks after the Perseus observation, a malfunction in the attitude control system put Hitomi into an uncontrollable spin that resulted in the break up and loss of the satellite.
“It is really disappointing that we have lost Hitomi and can’t go on with the programme that we had to look at many more clusters,” says Fabian.
The next mission that will be capable of fully following up the Hitomi programme is ESA’s Athena, an X-ray observatory scheduled for launch in the 2020s.
“Scientifically and technically, the Hitomi results are an exciting foretaste of Athena,” said David Lumb, ESA's Athena Study Scientist. “The demonstration of a radically new imaging spectrometer instrument concept gives huge confidence for future developments for Athena.”
Athena will have 100 times more collecting area and 100 times more pixels than Hitomi. Among the key scientific objectives of Athena are to investigate the evolution of clusters of galaxies including their interplay with energy injection from supermassive black holes.
“The Hitomi data show the potential that will be unleashed with Athena vastly increased imaging capability and sensitivity,” said Lumb.
Hitomi Collaboration. ‘The quiet intracluster medium in the core of the Perseus cluster.’ Nature (2016). doi:10.1038/nature18627.
Adapted from an ESA press release.
With its very first – and last – observation, the Hitomi x-ray observatory has discovered that the gas in the Perseus cluster of galaxies is much less turbulent than expected, despite being home to NGC 1275, a highly energetic active galaxy.This result is telling us that in terms of how cluster cores work, we have to think very carefully about what is going on.Andy FabianBackground: NASA/CXO; Spectrum: Hitomi Collaboration/JAXA, NASA, ESA, SRON, CSAX-ray view of the Perseus cluster
The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.
Astrophysics: Rare data from a lost satellite
Nature 535, 7610 (2016). doi:10.1038/535040a
Authors: Elizabeth Blanton
The Hitomi astronomical satellite observed gas motions in the Perseus galaxy cluster shortly before losing contact with Earth. Its findings are invaluable to studies of cluster physics and cosmology. See Letter p.117
Planetary science: Martian moons formed in situ
Nature 535, 7610 (2016). doi:10.1038/535011a
The moons of Mars may have formed from a disk of debris kicked up by the impact of a giant meteorite on the planet.Astronomers have struggled to explain the existence of Phobos (pictured) and Deimos, the small, irregularly shaped moons of the
Astrophysics: No neutrinos from black hole smash
Nature 535, 7610 (2016). doi:10.1038/535010c
The first hunt for neutrinos coming from the merger of two black holes — which last year produced the first direct detection of gravitational waves — has come up empty.Imre Bartos at Columbia University in New York and his colleagues analysed data from two