Institute of Astronomy

Astronomy News

First detection of gravitational waves and light produced by colliding neutron stars

6 hours 9 min ago

It could be a scenario from science fiction, but it really happened 130 million years ago -- in the NGC 4993 galaxy in the Hydra constellation, at a time here on Earth when dinosaurs still ruled, and flowering plants were only just evolving.

Today, dozens of UK scientists – including researchers from the University of Cambridge – and their international collaborators representing 70 observatories worldwide announced the detection of this event and the significant scientific firsts it has revealed about our Universe.

Those ripples in space finally reached Earth at 1.41pm UK time, on Thursday 17 August 2017, and were recorded by the twin detectors of the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and its European counterpart Virgo.

A few seconds later, the gamma-ray burst from the collision was recorded by two specialist space telescopes, and over following weeks, other space- and ground-based telescopes recorded the afterglow of the massive explosion. UK developed engineering and technology is at the heart of many of the instruments used for the detection and analysis.

Studying the data confirmed scientists’ initial conclusion that the event was the collision of a pair of neutron stars – the remnants of once gigantic stars, but collapsed down into approximately the size of a city. “These objects are made of matter in its most extreme, dense state, standing on the verge of total gravitational collapse,” said Michalis Agathos, from Cambridge’s Department of Applied Mathematics and Theoretical Physics. “By studying subtle effects of matter on the gravitational wave signal, such as the effects of tides that deform the neutron stars, we can infer the properties of matter in these extreme conditions.”

There are a number of “firsts” associated with this event, including the first detection of both gravitational waves and electromagnetic radiation (EM) - while existing astronomical observatories “see” EM across different frequencies (eg, optical, infra-red, gamma ray etc), gravitational waves are not EM but instead ripples in the fabric of space requiring completely different detection techniques. An analogy is that LIGO and Virgo “hear” the Universe.

The announcement also confirmed the first direct evidence that short gamma ray bursts are linked to colliding neutron stars. The shape of the gravitational waveform also provided a direct measure of the distance to the source, and it was the first confirmation and observation of the previously theoretical cataclysmic aftermaths of this kind of merger - a kilonova.

Additional research papers on the aftermath of the event have also produced a new understanding of how heavy elements such as gold and platinum are created by supernova and stellar collisions and then spread through the Universe. More such original science results are still under current analysis.

By combining gravitational-wave and electromagnetic signals together, researchers also used for the first time a new and novel technique to measure the expansion rate of the Universe.

While binary black holes produce “chirps” lasting a fraction of a second in the LIGO detector’s sensitive band, the August 17 chirp lasted approximately 100 seconds and was seen through the entire frequency range of LIGO — about the same range as common musical instruments. Scientists could identify the chirp source as objects that were much less massive than the black holes seen to date. In fact, “these long chirping signals from inspiralling neutron stars are really what many scientists expected LIGO and Virgo to see first,” said Christopher Moore, researcher at CENTRA, IST, Lisbon and member of the DAMTP/Cambridge LIGO group. “The shorter signals produced by the heavier black holes were a spectacular surprise that led to the awarding of the 2017 Nobel prize in physics.”

UK astronomers using the VISTA telescope in Chile were among the first to locate the new source. “We were really excited when we first got notification that a neutron star merger had been detected by LIGO,” said Professor Nial Tanvir from the University of Leicester, who leads a paper in Astrophysical Journal Letters today. “We immediately triggered observations on several telescopes in Chile to search for the explosion that we expected it to produce. In the end, we stayed up all night analysing the images as they came in, and it was remarkable how well the observations matched the theoretical predictions that had been made.”

“It is incredible to think that all the gold in the Earth was probably produced by merging neutron stars, similar to this event that exploded as kilonovae billions of years ago.”

“Not only is this the first time we have seen the light from the aftermath of an event that caused a gravitational wave, but we had never before caught two merging neutron stars in the act, so it will help us to figure out where some of the more exotic chemical elements on Earth come from,” said Dr Carlos Gonzalez-Fernandez of Cambridge’s Institute of Astronomy, who processed the follow-up images taken with the VISTA telescope.

“This is a spectacular discovery, and one of the first of many that we expect to come from combining together information from gravitational wave and electromagnetic observations,” said Nathan Johnson-McDaniel, researcher at DAMTP, who contributed to predictions of the amount of ejected matter using the gravitational wave measurements of the properties of the binary.

Though the LIGO detectors first picked up the gravitational wave in the United States, Virgo, in Italy, played a key role in the story. Due to its orientation with respect to the source at the time of detection, Virgo recovered a small signal; combined with the signal sizes and timing in the LIGO detectors, this allowed scientists to precisely triangulate the position in the sky. After performing a thorough vetting to make sure the signals were not an artefact of instrumentation, scientists concluded that a gravitational wave came from a relatively small patch of the southern sky.

“This event has the most precise sky localisation of all detected gravitational waves so far,” says Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam, who is the spokesperson for the Virgo collaboration. “This record precision enabled astronomers to perform follow-up observations that led to a plethora of breath-taking results.”

Fermi was able to provide a localisation that was later confirmed and greatly refined with the coordinates provided by the combined LIGO-Virgo detection. With these coordinates, a handful of observatories around the world were able, hours later, to start searching the region of the sky where the signal was thought to originate. A new point of light, resembling a new star, was first found by optical telescopes. Ultimately, about 70 observatories on the ground and in space observed the event at their representative wavelengths. “What I am most excited about, personally, is a completely new way of measuring distances across the universe through combining the gravitational wave and electromagnetic signals. Obviously, this new cartography of the cosmos has just started with this first event, but I just wonder whether this is where we will see major surprises in the future,” said Ulrich Sperhake, Head of Cambridge’s gravitational wave group in LIGO.

In the weeks and months ahead, telescopes around the world will continue to observe the afterglow of the neutron star merger and gather further evidence about its various stages, its interaction with its surroundings, and the processes that produce the heaviest elements in the universe.

Reference: 
Physical Review Letters
"GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral."

Science
"A Radio Counterpart to a Neutron Star Merger."
"Swift and NuSTAR observations of GW170817: detection of a blue kilonova."
"Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger."

Astrophysical Journal Letters
"Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A."
"Multi-Messenger Observations of a Binary Neutron Star Merger."

Nature
"A gravitational-wave standard siren measurement of the Hubble constant."

Adapted from STFC and LIGO press releases. 

In a galaxy far away, two dead stars begin a final spiral into a massive collision. The resulting explosion unleashes a huge burst of energy, sending ripples across the very fabric of space. In the nuclear cauldron of the collision, atoms are ripped apart to form entirely new elements and scattered outward across the Universe. 

What I am most excited about, personally, is a completely new way of measuring distances across the universe.Ulrich SperhakeESO/L. Calçada/M. KornmesserArtist’s impression of merging neutron stars


The text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Gravitational waves have let us see huge neutron stars colliding

6 hours 10 min ago

We’ve taken the first pictures of neutron stars colliding 130 million light years away. The resulting gravitational waves may solve some big cosmic mysteries

NASA Missions Catch First Light from a Gravitational-Wave Event

6 hours 10 min ago
For the first time, NASA scientists have detected light tied to a gravitational-wave event, thanks to two merging neutron stars in the galaxy NGC 4993, located about 130 million light-years from Earth in the constellation Hydra.

ESO Telescopes Observe First Light from Gravitational Wave Source

6 hours 11 min ago
ESO’s fleet of telescopes in Chile have detected the first visible counterpart to a gravitational wave source. These historic observations suggest that this unique object is the result of the merger of two neutron stars. The cataclysmic aftermaths of this kind of merger — long-predicted events called kilonovae — disperse heavy elements such as gold and platinum throughout the Universe. This discovery, published in several papers in the journal Nature and elsewhere, also provides the strongest evidence yet that short-duration gamma-ray bursts are caused by mergers of neutron stars.

INTEGRAL sees blast travelling with gravitational waves

6 hours 11 min ago

ESA's INTEGRAL satellite recently played a crucial role in discovering the flash of gamma rays linked to the gravitational waves released by the collision of two neutron stars.

Hubble observes source of gravitational waves for the first time [heic1717]

6 hours 11 min ago

The NASA/ESA Hubble Space Telescope has observed for the first time the source of a gravitational wave, created by the merger of two neutron stars. This merger created a kilonova – an object predicted by theory decades ago – that ejects heavy elements such as gold and platinum into space. This event also provides the strongest evidence yet that short duration gamma-ray bursts are caused by mergers of neutron stars. This discovery is the first glimpse of multi-messenger astronomy, bringing together both gravitational waves and electromagnetic radiation.

Dead star merger ripples across space

6 hours 12 min ago

Scientists detect the warping of space generated by the collision of two neutron stars.

Neutron stars: 'Hear' the mighty cosmic collision

6 hours 13 min ago

Scientists convert the gravitational wave signal from merging neutron stars into sound.

We can finally map the spiral arm on the far side of the galaxy

13 October 2017 - 9:26am

Using a jet of radio waves, astronomers have begun to map the other side of the Milky Way. Within 10 years we could have a complete map of the entire galaxy

The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation

12 October 2017 - 9:34am
Haumea—one of the four known trans-Neptunian dwarf planets—is a very elongated and rapidly rotating body. In contrast to other dwarf planets, its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system, and the Centaur Chiron was later found to possess something similar to Chariklo’s rings. Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multi-chord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea’s equator and the orbit of its satellite Hi’iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea’s spin period—that is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea’s largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates. In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen- or methane-dominated atmosphere was detected.

Astronomy: Ring detected around a dwarf planet

12 October 2017 - 9:33am
Observations of the distant dwarf planet Haumea constrain its size, shape and density, and reveal an encircling planetary ring. The discovery suggests that rings are not as rare in the Solar System as previously thought. See Letter p.219

Giant Exoplanet Hunters: Look for Debris Disks

12 October 2017 - 9:30am

There's no map showing all the billions of exoplanets hiding in our galaxy -- they're so distant and faint compared to their stars, it's hard to find them. Now, astronomers hunting for new worlds have established a possible signpost for giant exoplanets.

News Article Type: Homepage ArticlesPublished: Wednesday, October 11, 2017 - 14:14

Distant dwarf planet near Pluto has a ring that no one expected

12 October 2017 - 9:29am

The tiny world Haumea has a ring, the most distant we’ve found in our solar system. This may mean rings encircle other far-off worlds in the solar system

Asteroid close approach to test warning systems

12 October 2017 - 9:27am

A house-sized asteroid passes close to Earth, allowing scientists to rehearse future strike threats.

Giant black hole seen flickering on and off after galaxy snack

11 October 2017 - 9:18am

Active Galactic Nuclei occur when a black hole devours a cloud of gas and dust and shines really brightly. Now one has been seen doing it twice

Far-infrared Instrument to Map Star Formation in the Universe

11 October 2017 - 9:17am

Technology Development: Questions about how and when stars are formed continue to tug at human curiosity. Star formation is governed by gravity and heat. Gravity causes molecular clouds to collapse and eventually form stars and planetary systems, but to complete the process, heat needs to be continuously removed from the cloud. Hence, ionized carbon and neutral oxygen—the two major coolants of the interstellar medium (ISM)—are the best indicators of star-forming regions. New technology is being developed that will allow spaceborne telescopes to make high-resolution multi-pixel maps of the universe, which will help scientists understand why star and planet formation is common in some regions of the universe, while other regions are dormant.

Close-up of a Schottky diode, showing the
air-bridge that connects the anode.

The technology utilizes state-ofthe- art Schottky diodes that enable a space telescope to observe and map deep-space regions. The Schottky diodes work at the frequencies required to detect ionized carbon and neutral oxygen—1.9 and 2.06 THz respectively. The smallest feature of these diodes is less than one micron (a human hair is typically 50 microns in diameter).

To date, only a single-pixel receiver has been flown in space. The multi-pixel technology NASA is developing allows tens and hundreds of these Schottky diodes to be packaged in metal enclosures, which will allow scientists to map large areas of the sky simultaneously. In 2016, NASA researchers demonstrated the first 16-pixel camera that worked at 1.9 THz. To implement multi-pixel THz cameras, the development team investigated a concept for packaging the diodes in very precisely machined thin metallic plates that are then stacked. To create a 16-pixel source, five metal plates—each about 5 mm thick—must be machined very precisely to obtain alignment tolerances better than 10 microns.

This 16-pixel module is made with 5 metal
plates that are precisely machined to achieve
alignment tolerance better than 10 microns.

Impact: This multi-pixel far-infrared technology will enable NASA space telescopes to take “pictures” of the universe that will allow scientists to better understand the chemical and physical processes involved in the birth of new stars.

Status and Future Plans: Now that the first 16-pixel camera has been demonstrated, the NASA team is working to increase the sensitivity and pixel count so that the technology can be used on future NASA space missions.

Sponsoring Organization: The Astrophysics Division’s SAT program provides funding for this technology development effort to project lead Imran Mehdi at NASA Jet Propulsion Laboratory (JPL).

Read more Technology Stories

Master Image: 

Exploding stars could have kick-started our ancestors’ evolution

10 October 2017 - 9:15am

The savannahs early hominins occupied might have appeared thanks to a spate of wildfires 8 million years ago – which might in turn be linked to a nearby supernova

Nanoflares in the sun’s plasma may cause its scalding atmosphere

10 October 2017 - 9:14am

Tiny explosions in the atmosphere may explain why the solar corona is a million degrees hotter than the sun’s surface

Giant black hole seen flickering on and off after galaxy snack

10 October 2017 - 9:13am

Active Galactic Nuclei occur when a black hole devours a cloud of gas and dust and shines really brightly. Now one has been seen doing it twice

The Scientific Quest to Explain Kepler’s Most Enigmatic Find

9 October 2017 - 9:27am

Some 1,500 light years from Earth, a mystery of stellar proportions is playing out. A singular star out there captured scientists’ and the public’s imagination in September 2015 with its strangely fluctuating brightness.

News Article Type: Homepage ArticlesPublished: Friday, October 6, 2017 - 11:32