astronomy (3)


An artist's impression of the planetesimal orbiting on a 2-hour period within the gaseous disc around SDSS J1228+1040 (by Mark Garlick).


Topics: Astronomy, Astrophysics, Exoplanets, Spectrograph, White Dwarfs

When the hydrogen fuel that keeps a star like our sun burning brightly is exhausted, the star expands into a red giant before collapsing into a hot, dense white dwarf. Although the stellar swelling engulfs nearby planets, theoretical models suggest that some planets and planetary cores up to hundreds of kilometers in diameter can survive the star’s death and fall into closer orbit. But identifying solid bodies around a dim stellar core is difficult. Now Christopher Manser (University of Warwick) and colleagues have used a new spectroscopic method to identify a planetesimal orbiting a white dwarf 400 light-years from our solar system.

Astronomers have discovered most exoplanets—including an asteroid-like body orbiting a white dwarf—via the transit method, identifying periodic dimming as an object passes in front of its host star. But the method requires a lucky geometry of the planetary system’s orbital plane relative to Earth. Manser and his team instead turned to short-cadence optical spectroscopy using data from the 10.4 m Gran Telescopio Canarias in Spain. They focused on one of just a few white dwarfs that, based on metal emission lines in the stellar and disk spectra, are suspected to be surrounded by disks of gas and dust. Minute-by-minute observations over several nights in 2017 and 2018 let the researchers deconstruct the light emanating from the disk and determine how much variation had occurred over a year.


A glimpse of a planetary system’s final stages, Rachel Berkowitz, Physics Today

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Lumpy Neutron Stars...

An artist’s rendition of a neutron star. Credit: Kevin Gill Flickr (CC by 2.0)


Topics: Astronomy, Astrophysics, Einstein, Gravitational Waves, Neutron Stars

Gravitational waves—the ghostly ripples in spacetime first predicted by Einstein and finally detected a century later by advanced observatories—have sparked a revolution in astrophysics, revealing the otherwise-hidden details of merging black holes and neutron stars. Now, scientists have used these waves to open another new window on the universe, providing new constraints on neutron stars' exact shapes. The result will aid researchers in their ongoing quest to understand the inner workings of these exotic objects.

So far, 11 gravitational-wave events have been detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) interferometers in Washington and Louisiana and the Virgo gravitational-wave observatory in Italy. Of these events, 10 came from mergers of binary black holes, and one from the merger of two neutron stars. In all cases, the form of the waves matched the predictions of Einstein's theory of general relativity.

For the binary black hole events, the passing waves lasted less than a second; for the merging neutron stars, the emissions occurred for about 100 seconds. But such rapid pulses aren't the only types of gravitational waves that could be streaming through the universe. In particular, solitary neutron stars might be emitting detectable gravitational waves as they spin—signals that could reveal important new details of the stars' topography and internal composition.


Gravitational Observatories Hunt for Lumpy Neutron Stars
David Appell, Scientific American

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Sagittarius A...

Getty Images

Topics: Astronomy, Astrophysics, Black Holes, Cosmology, Einstein

They've captured our imaginations for decades, but we've never actually photographed a black hole before – until now.

Next Wednesday, at several press briefings around the world, scientists will apparently unveil humanity's first-ever photo of a black hole, the European Space Agency said in a statement. Specifically, the photo will be of "Sagittarius A," the supermassive black hole that's at the center of our Milky Way galaxy.

But aren't black holes, well, black, and thus invisible, so none of our telescopes can "see" them? Yes – therefore the image we're likely to see will be of the "event horizon," the edge of the black hole where light can't escape. [1]


Next week, a collection of countries around the world are going to make a big announcement, and no one is sure exactly what it’s going to be. However, there are some possibilities, and the most exciting one is that they are about to reveal the first-ever photograph of the event horizon of a black hole.

Taking a photo of a black hole is not an easy task. Not only are black holes famous for not letting any light escape, even the nearest known black holes are very far away. The specific black hole astronomers wanted to photograph, Sagittarius A*, lies at the center of our galaxy 25,000 light-years away.

The international Event Horizon Telescope project announced its plan to photograph Sagittarius A* back in 2017, and they enlisted some of the world’s biggest telescopes to help out. The researchers used half a dozen radio telescopes, including the ALMA telescope in Chile and the James Clerk Maxwell telescope in Hawaii, to stare at Sagittarius A* over the past two years.

And while a picture of the black hole itself is impossible, the EHT astronomers were really aiming at the next best thing: the event horizon, the border of the black hole beyond which not even light can escape. At the event horizon, gravity is so strong that light will orbit the black hole like planets orbit stars, and our telescopes should be able to pick that up. [2]

1. 'Something no human has seen before': The first-ever photograph of a black hole will likely be unveiled next week, Doyle Rice, USA Today
2. We Might Be About to See the First Ever Photo of a Black Hole, Avery Thomson, Popular Mechanics

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