Red giant and neutron star interaction

Donor star breathes life into zombie companion

ESA’s Integral space observatory has witnessed a rare event: the moment that winds emitted by a swollen red giant star revived its slow-spinning companion, the core of a dead star, bringing it back to life in a flash of X-rays. The X-ray flare was first detected by Integral on 13 August 2017 from an unknown source in the direction of the crowded centre of our Milky Way. The sudden detection triggered a slew of follow-up observations in the following weeks to pin down the culprit. The observations revealed a strongly magnetised and slowly rotating neutron star that had likely just begun to feed on material from a neighbouring red giant star.

Stars the mass of our Sun, and up to eight times more massive, evolve into red giants towards the end of their lives. Their outer layers puff up and expand millions of kilometres, their dusty, gassy shells blown away from the central star in relatively slow winds up to few hundreds of km/s.

Stellar evolution Even larger stars, up to 25–30 times more massive than the Sun, race through their fuel and explode in a supernova, sometimes leaving behind a spinning stellar corpse with a strong magnetic field, known as a neutron star. This tiny core packs the mass of nearly one and half Suns into a sphere only 10 km across, making them some of the densest celestial objects known. It is not uncommon to find stars paired together, but the new system of a neutron star and red giant is a particularly rare breed known as a ‘symbiotic X-ray binary’, with no more than 10 known. “Integral caught a unique moment in the birth of a rare binary system,” says Enrico Bozzo from University of Geneva and lead author of the paper that describes the discovery. “The red giant released a sufficiently dense slow wind to feed its neutron star companion, giving rise to high-energy emission from the dead stellar core for the first time.”

The pairing is certainly peculiar. ESA’s XMM-Newton and NASA’s NuSTAR space telescopes showed that the neutron star spins almost every two hours – very slow compared with other neutron stars, which can spin up to many times per second. Then, the first measurement of the magnetic field of such a neutron star revealed it to be surprisingly strong. A strong magnetic field typically points to a young neutron star – the magnetic field is thought to fade over time – while a red giant is much older, making it a bizarre couple to have grown up together. “These objects are puzzling,” says Enrico. “It might be that either the neutron star magnetic field does not decay substantially with time after all, or the neutron star actually formed later in the history of the binary system. That would mean it collapsed from a white dwarf into a neutron star as a result of feeding off the red giant over a long time, rather than becoming a neutron star as a result of a more traditional supernova explosion of a short-lived massive star.” With a young neutron star and an old red giant, at some point the winds travelling from the puffed-up giant will begin to rain on to the smaller star, slowing its spin and emitting X-rays. “We haven’t seen this object before in the past 15 years of our observations with Integral, so we believe we saw the X-rays turning on for the first time,” says Erik Kuulkers, ESA’s Integral project scientist. “We’ll continue to watch how it behaves in case it is just a long ‘burp’ of winds, but so far we haven’t seen any significant changes.”

Notes for Editors “IGR J17329-2731: the birth of a symbiotic X-ray binary,” by E. Bozzo et al is accepted for publication in Astronomy & Astrophysics. The rapid response of the follow-up observations was enabled by the SmartNet community. This included important contributions from ESA’s XMM-Newton and NASA’s NuSTARand Swift space telescopes, and the ground-based Southern Astrophysical Research Telescope, Faulkes Telescopes North and South and the Las Cumbres Observatory. For further information, please contact:

Enrico Bozzo

University of Geneva, Switzerland

Email: enrico.bozzo@unige.ch Erik Kuulkers

ESA Integral project scientist

Email: erik.kuulkers@esa.int Markus Bauer

ESA Science Communication Officer

Tel: +31 71 565 6799

Mob: +31 61 594 3 954

Email: markus.bauer@esa.int </s> An Indian scientist recently discovered 15 repeating radio bursts emitted by a dwarf galaxy after observing it for five hours.

Here's all you need to know about the finding:

1. This discovery was made by Breakthrough Listen postdoctoral researcher Vishal Gajjar, who was detecting extraterrestrials. The dwarf galaxy that gave out these 15 electromagnetic emissions is located at a distance of around 3 million light years from Earth.

2. Breakthrough Listen was launched in 2015 as an initiative to find signs of intelligent life in the universe. As per the hypotheses of the researchers, these emissions could be from an energy source that is being utilised by extraterrestrial civilisations to fuel their spaceships.

"Bursts from this source have never been seen at this high a frequency," said Andrew Siemion, director of the Berkeley SETI Research Centre and a member of the Breakthrough Listen programme.

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3. "When the recently-detected pulses left their host galaxy, our entire Solar System was just 2 billion years old," said Breakthrough Listen in a statement, referring to the 15 fast radio bursts (FRBs).

It added: "Life on Earth consisted of only single-celled organisms, and it would be another billion years before even the simplest multi-cellular life began to evolve."

4. The Parkes Telescope in Australia had spotted FRBs for the first time. The phenomenon was later observed by numerous radio telescopes across the world. FRBs are basically radiant emissions from distant galaxies.

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5. The sources of FRBs are distant and usually unidentified. Discovered on November 2, 2012, FRB 121102 is believed to be the source of these 15 radio bursts. FRB 121102 is the only one known to repeat: More than 150 high-energy bursts have been observed coming from the object. It was identified last year as a dwarf galaxy located 3 million light years from Earth.

6. Researchers are trying to understand what leads to the formation of FRBs, and the dwarf galaxy has turned into the main target for all the monitoring operations carried out across the world.

"As well as confirming that the source is in a newly active state, the high resolution of the data obtained by the Listen instrument will allow measurement of the properties of these mysterious bursts at a higher precision than ever possible before," said the Breakthrough Listen statement. </s> July 2 (UPI) -- The European Southern Observatory's Very Large Telescope has captured detailed imagery of a newborn planet carving a path through the protoplanetary disk surrounding PDS 70, a young dwarf star.

According to ESO, the observations -- captured by SPHERE, VLT's planet-hunting instrument -- included the "first confirmed image of a planet caught in the act of forming in the dusty disc surrounding a young star."

The telescope's SPHERE instrument was able to observe the exoplanet at multiple wavelengths, revealing the young planet's atmosphere.

The observations suggest PDS 70b is a giant gas planet several times more massive than Jupiter. The exoplanet boasts a surface temperature of roughly 1000 degrees Celsius, more than twice as hot as Mercury, the hottest planet in our solar system.

SPHERE uses multi-wavelength observations, a coronagraph and a technique called high-contrast imaging to filter out the signal of faint exoplanets circling bright stars. The coronagraph, which appears as a dark circle in the middle of the VLT image, works to block out the bright light of the host star -- emissions that would otherwise overwhelm the telescope's ability to photograph and analyze the characteristics of the protoplanetary disk.

The new image suggests the newborn planet has created sizable gaps in the protoplanetary disk.

"Keppler's results give us a new window onto the complex and poorly-understood early stages of planetary evolution," André Müller, a researcher at the Max Planck Institute for Astronomy, said in a news release. "We needed to observe a planet in a young star's disc to really understand the processes behind planet formation."

Data revealing the chemical makeup of the exoplanet's atmosphere will help scientists model the gas giant's formation and early evolution.

Scientists detailed their discovery and analysis of PDS 70b in a pair of papers, soon to be published in the journal Astronomy and Astrophysics.
European astronomers observe the "birth" of a symbiotic X-ray binary, IGR J17329-2731, described as a transient, from the Galactic Center using INTEGRAL space telescope.