Tag Archives: LIGO

At last, we’ve found gravitational waves from a collapsing pair of neutron stars

The Conversation

File 20171015 1505 1tylrql.jpg?ixlib=rb 1.1
Artist’s impression of the collision of two neutron stars, the source of the latest gravitational waves detected. National Science Foundation/LIGO/Sonoma State University/A. Simonnet, Author provided

David Blair, University of Western Australia

After weeks of rumour and speculation, scientists have today finally announced the death spiral of two neutron stars as a source of gravitational waves.

It’s among the biggest news for science in decades, because the findings help shed light on many aspects of astrophysics, including the origins of cosmic explosions known as gamma-ray bursts and of some heavy elements in the universe, such as gold.

The latest detection has scientists excited because most predictions had favoured the detection of gravitational waves from coalescing pairs of neutron stars. Yet the first and all subsequent detections prior to today’s announcement had only come from collisions of black holes.

Read more: We beat a cyber attack to see the ‘kilonova’ glow from a collapsing pair of neutron stars

The first detection

It was back in 2015 when the Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) detectors heard the whoop of the first gravitational wave signal ever detected.

The sound of two black holes colliding.
LIGO163 KB (download)

That came from the collision of a pair of black holes in the distant universe about 1.3 billion light years away. Suddenly we knew that our detectors worked; suddenly we knew that the black holes of Einstein’s theory are really out there. Suddenly the dream of gravitational wave astronomy became reality.

The first strong signal was so surprising that the international teams at the LIGO observatories spent weeks trying to work out if someone could have secretly put signals into the data!

Since then there have been more black hole signals, but there was no sign of the predicted neutron stars.

An artist’s conception of two merging black holes similar to those detected by LIGO. LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

The neutron star connection

Physicists have long considered neutron stars to be perfect sources of gravitational waves.

Neutron stars are balls of neutrons, about the size of a city but weighing in at about 1.4 times the mass of our Sun.

The first neutron star was discovered by Jocelyn Bell Burnell in 1967, and in 1974 Russell Hulse and Joseph Taylor found a pair of neutron stars spiralling slowly together in the Milky Way, a discovery that led to their Nobel Prize in Physics in 1993.

Caltech physicist Kip Thorne – one of three people awarded this year’s Nobel Prize for Physics – led a campaign to build huge laser interferometers, optimised for detecting the final death spiral of a pair of neutron stars.

Barry Barish (another of this year’s Nobel Prize winners) internationalised the LIGO observatories, bringing Britain, Germany and Australia into the collaboration.

More than just a wave

During the decades of development of gravitational wave detectors, astronomers had become fascinated by vast bursts of gamma rays coming in from the distant universe at the rate of about one every day.

Israeli physicist Tsvi Piran proposed in 1989 that some of these bursts could be created by coalescing neutron stars. If this was the case, then bursts of gravitational waves would be accompanied by bursts of gamma rays.

Many astrophysicists modelled the violent coalescence of merging neutron stars. Some of the superdense neutron rich matter would be flung into space, where it would be relieved of the massive pressure inside the neutron stars.

Uncompressed, it would go off like a vast nuclear fission bomb, creating a slew of heavy elements such as gold and platinum. Within minutes a hot fireball would shine brightly, powered by the decaying radioactivity of the new formed elements.

A new signal detected

Advanced LIGO‘s two 4km detectors in the United States have been operating since 2015. The 3km Advanced Virgo detector in Europe came online on August 1 this year.

Europe’s Virgo becomes the third detector in the hunt for gravitational waves. The Virgo collaboration

Many optical telescopes had signed up to receive any alerts from LIGO and Virgo.

Meanwhile, NASA’s orbiting gamma ray telescopes Fermi and Swift continued their continuous monitoring of the skies. Billions of dollars worth of astronomical hardware was poised and ready in August 2017.

Thursday August 17, 2017, was the day our detectors registered a slowly rising siren call that lasted for a minute and finished with a sharp crescendo.

It wasn’t the brief whoop of a pair of large black holes but the much slower death song of a pair of neutron stars with total mass about three times the mass of the Sun. Two seconds later the Fermi satellite detected a short gamma ray burst. Within minutes the source direction had been roughly localised.

The alert goes out

Within 30 minutes alerts went out to telescopes across the planet. Telescope schedules were interrupted, and before long a bright new object was found in galaxy NGC 4993, seen in the Hydra constellation, and visible in the southern hemisphere in August.

This simulation shows the final stages of the merging of two neutron stars.

The new object decayed away exponentially over a few days as might be expected for a radioactively powered nebula.

NGC 4993 is 130 million light years away. The arrival of gravity waves and gamma rays within 2 seconds of each other tells us that to a precision of a part in a million billion, both types of wave travel at the same speed.

Read more: After the alert: radio ‘eyes’ hunt the source of the gravitational waves

The fact that two completely different types of radiation, one that is a ripple of space itself, and the other that travels through space, should travel at exactly the same speed could seem astonishing, yet it is exactly what Einstein predicted.

The event is a treasure trove of astrophysics. From one faint gravitational sound, a momentary burst of gamma rays and the faint fading glow of exploding nuclear matter, we have the first direct measurement of the distance of galaxies.

This is because gravitational wave signals directly encode distance. And suddenly we know how gamma ray bursts are created. And suddenly we know that all our gold, our rings and treasures, was probably created in neutron star collisions.

The ConversationIt will take many years to fully explore the data, and meanwhile more and more data will flood in as we continue to open the gravitational wave spectrum with more observatories on earth and in space. The new era of multi-messenger astronomy has begun!

David Blair, Director, WA Node of the ARC Centre of Excellence for Gravitational Wave Discovery, and the Australian International Gravitational Research Centre, University of Western Australia

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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2016: the year in space and astronomy

The Conversation

Alan Duffy, Swinburne University of Technology and Rebecca Allen, Swinburne University of Technology

The achievements of astrophysicists this year were as groundbreaking as they were varied. From reuniting a lander with a mothership on a comet, to seeing the most extreme cosmic events with gravitational waves, 2016 was truly out of this world for science.

Here are some of the highlights of the year that was.

1. Gravitational Waves

The spectacular announcement that ripples in the very fabric of spacetime itself had been found (and from surprisingly massive black holes colliding) sent similarly massive ripples through the scientific community. The discovery was made using the Laser Interferometer Gravitational-Wave Observatory (LIGO) and represents a fundamentally new sense with which to see the universe.

Animation showing how colliding black holes cause a ripple in spacetime that moves outwards into the universe as a gravitational wave.

The gravitational waves cause one arm of the LIGO detector to stretch relative to the other by less than a thousandth of the width of a proton in the centre of the atom. Relatively speaking, that’s like measuring a hair’s-width change in the distance to the nearest star.

This discovery was the end of a century-long quest to prove Einstein’s final prediction that these gravitational waves are real. It also allows us to directly “see” that famously and fundamentally invisible entity: the black hole (as well as definitively proving its existence). The fact that the two black holes collided 1.3 billion years ago and the waves swept through Earth just days after turning the detector on only add to the incredible story of this discovery.

The ‘sound’ of the black holes colliding where the measured signal from LIGO is converted to audio, the rising chirp sound towards the end is the two black holes spiralling together ever more quickly. A surprisingly wimpy sound for the most extreme collision ever detected.

2. SpaceX lands (and crashes) a rocket

The year started so well for SpaceX with the incredible achievement of sending a satellite into orbit, which is no mean feat itself at such low cost, before then landing that launch rocket on a barge in the ocean. A seemingly unstoppable sequence of launches and landings made it appear that a new era of vastly cheaper access to space through rockets that could be refuelled and reused was at hand.

A Falcon 9 first-stage automatically returns to the barge/droneship ‘Of Course I Still Love You’ in the middle of the Atlantic ocean.

Unfortunately, with the explosion of a Falcon 9 on the launchpad, the company was grounded, but apparently hopes for a resumed launch in early January.

SpaceX outlines a vision for travel to Mars with planned Interplanetary Transport System.

Add to that the visionary plans to settle Mars outlined by Elon Musk, albeit not without some audacious challenges, and it’s been a year of highs and lows for SpaceX.

3. Closest star may harbour Earth-like world

Proxima Centauri is our Sun’s nearest neighbour at just over four light years away, and it appears that its solar system may contain an Earth-like world. Until this year, astronomers weren’t even sure that any planets orbited the star, let alone ones that might harbour the best extrasolar candidate for life that spacecraft could visit within our lifetime.

What a trip to the Sun’s closet neighbour would look like.

The planet, creatively named “Proxima b”, was discovered by a team of astronomers at Queen Mary University in London. Using the light of Proxima Centauri, the astronomers were able to detect subtle shifts in the star’s orbit (seen as a “wobble”), which is the telltale sign that another massive object is nearby.

An artist’s impression of Proxima b’s landscape. ESO/M. Kornmesser

While Proxima Centauri is barely 10% the size of our Sun, Proxima b’s orbit is only 11 days long, meaning it is very close to the star and lies just within the so-called habitable zone. However, follow-up with either Hubble or the upcoming James Webb Space telescope is necessary to determine if the exoplanet is as well suited for life as Earth.

4. Breakthrough Listen listening and Starshot star-ted

With a potential Earth twin identified in Proxima b, now the challenge is to reach it within a human lifetime. With the breakthrough initiative starshot, which has been funded by Russian billionaire Yuri Milner and endorsed by none other than Stephen Hawking, lightweight nanosails can be propelled by light beams to reach speeds up to millions of kilometres an hour.

Such speeds would allow a spacecraft to arrive at Proxima b in about 20 years, thus enabling humans to send information to another known planet for the first time.

However, there are many challenges ahead, such as the fact that the technology doesn’t exist yet, and that high-speed collisions with gas and dust between stars may destroy it before it can reach its target.

But humans have proven to be resourceful, and key technology is advancing at an exponential rate. Incredibly the idea of sailing to another world is no longer science fiction, but rather an outrageously ambitious science project.

One of the founders of the Breakthrough initiatives, Yuri Milner, discusses the technology needed for breakthrough starshot.

Perhaps, aliens are already sending out their own information in the form of radio transmissions. In another breakthrough initiative called Listen, also championed by Hawking, astronomers will be searching the habitable zones around the million closest stars to try to detect incoming radio transmissions. Involving Australia’s very own Parkes telescope (as well as the Green Bank Telescope and Lick Observatory at visible wavelengths of light), observations have been running through 2016 and the search for alien signals will continue for the next decade.

5. Philae reunited with Rosetta

In 2014 the Philae lander became the first space probe to land on a comet, and even though its crash landing dictated that its science transmission would be a one-off, its recent rediscovery by Rosetta has allowed it to continue to contribute to analysis of comet 67P.

Philae’s crash location, as well as the orientation of the doomed probe, has allowed astronomers to accurately interpret data taken by Rosetta regarding the composition of the comet.

Where’s Philae? ESA

While Philae has literally been living under (crashed on) a rock for the past two years, Rosetta has been the busy bee, taking numerous images, spectroscopy and other data of the comet.

In fact, data taken from Rosetta’s spectrometer has been analysed and revealed that the amino acid, glycine, is present in the comet’s outgassing, which breaks away from the surface of the comet as it becomes unstable from solar heating. Glycine is one of the fundamental building blocks of life; necessary for proteins and DNA, and its confirmed extraterrestrial confirms that the ingredients for life are unique to Earth, and that we may have comets to thank for providing our microbial ancestors with those crucial ingredients.

Dust and gas emitted from comet 67P reveal an amino acid. ESA

Outlook for Down Under

The future for astrophysics in Australia in 2017 looks particularly bright, with two ARC Centres of Excellence: CAASTRO-3D studying the build of atoms over cosmic time; and OzGRav exploring the universe with gravitational waves; as well as SABRE, the world’s first dark matter detector in the Southern Hemisphere, installed by end of the year.

If you thought 2016 was a great year in space, then you’re in for a treat in 2017.

The ConversationAlan Duffy, Research Fellow, Swinburne University of Technology and Rebecca Allen, PhD candidate researching galaxy formation and evolution, Swinburne University of Technology

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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ASU’s Krauss hails discovery, which he predicted, as important as the invention of the telescope

Everything shifted this morning.

In the 100th-anniversary year of Einstein’s theory of relativity, scientists announced they have proved it.

Using a stunning display of technological prowess, a group of physicists measured gravitational waves, a ripple in the fabric of space caused by the collision of two immense objects far out in the universe.

The discovery is on par with the invention of the telescope, said Lawrence Krauss, a theoretical physicist and cosmologist at Arizona State University.

“It heralds what I think is the beginning of the new astronomy for the 21st century,” Krauss said. “Gravitational-wave astronomy will be the astronomy of the 21st century. It’s opened a new window on the universe, just like the telescope in some sense or when we first used radio waves to explore the universe.”

Researchers at the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), a joint project between the Massachusetts Institute of Technology and the California Institute of Technology, used two detectors at opposite ends of the country to measure a change in length down to a tolerance of one ten-thousandth of a proton.

“Using gravitational waves to explore the universe will allow us to see things we could have never seen before,” Krauss said. “We’ll be exploring science in a domain we’ve never seen before. It will also allow us to explore objects in the universe we’ve never seen before.”

The LIGO experiment observed the collision of two black holes. Black holes are at the center of virtually every large galaxy, and their dynamics may be related to the dynamics of galaxy formation. It’s a chicken-and-egg question: Which formed first?

Two incredibly immense black holes collided, converting a mass three times the size of the sun into energy in a single second, sending out a ripple in space and time.

“It allows us to see things that are just truly mind-boggling,” Krauss said. “A black hole with a mass 39 times the mass of our sun collides with another black hole 26 times the mass of the sun, comes together to make one big black hole that’s 62 times the mass of the sun. If you do your addition, 62 is not 39 plus 26, it’s three solar masses smaller. Three solar masses of energy went in a second into gravitational waves. … Our sun over 10 billion years is only going to convert a small fraction of its mass into energy by burning 100 million hydrogen bombs every second. But in one second or so, in a very short time — BOOM — three times the mass of the sun was converted by E=mc² into energy. It’s unfathomable. It just disappeared. Imagine our sun just disappearing in a second.”

“Gravitational-wave astronomy will be the astronomy of the 21st century. It’s opened a new window on the universe, just like the telescope in some sense or when we first used radio waves to explore the universe.” — tweet by Lawrence Krauss, ASU theoretical physicist and cosmologist

They fired lasers down the arms and bounced them off mirrors at either end. The laser path lengths are equal under normal circumstances, but not when a gravitational wave passes through.

“It’s a testament to human perseverance and ingenuity,” Krauss said. “What was required to build a detector to detect gravitational waves is unbelievable.”

It’s like being in California and detecting a leaf falling in Virginia. The system is so sensitive a truck hitting a pothole miles away threw it off in the early years when it started operating in 2002. The arms are so long that the curvature of the Earth is a measurable 1 meter (vertical) difference over the 4-kilometer length of each arm. “The most precise concrete pouring and leveling imaginable was required to counteract this curvature and ensure that LIGO’s vacuum chambers were truly ‘flat’ and level,” the lab’s website said. The detectors are so precise continental drift had to be taken into consideration, Krauss said.

“They had to be able to measure the change in length of a 4-kilometer-long tunnel by an amount equal to one ten-thousandth the size of a proton,” he said. “When you say that, it’s just amazing. It’s just amazing that human beings could do that. They had to push quantum technology to its limits. Even the quantum fluctuations of atoms in the mirror are such that even those have to be controlled. It’s just amazing what they can do. It’s proof that truth is stranger than fiction. Science-fiction writers wouldn’t dare to even propose it, but it’s been done. It’s taken 20 years of hard work by thousands of physicists; there are more than 1,000 people working on that collaboration.”

LIGO will allow the laws of physics to be tested in domains never seen before, like the event horizon of black holes, “which is that region inside of which you never get out, and which, if you’re near, strange things happen — if you’ve seen the movie ‘Interstellar,’ time dilates and everything else,” Krauss said. “It’ll be a whole new type of astronomy.”

He appreciated the poetics of the discovery happening in the anniversary year of relativity.

“It’s beautifully fitting that on the 100th anniversary of the development of general relativity, when Einstein first proposed the existence of gravitational waves, that they’ve finally been directly discovered,” he said. “It’s superlatives all over. It’s an amazing piece of work by an amazing group of scientists who were dedicated to doing something that appeared impossible, to discover something that opens a new window on the universe. And every time we open a new window on the universe, we’ve been surprised. I’m sure there will be surprises.”

Krauss has taken abuse from some quarters for teasing the announcement on his Twitter feed, once this past September and again in January. (One astrophysicist claimed to be “appalled” by the tweets.) Krauss thought drumming up interest in a major discovery was the right thing to do.

“If scientists are excited, I didn’t see why the public shouldn’t be,” he said. “No one on the project told me anything in confidence. I just heard the rumor, and it turned out to be true. … The net result was hundreds of articles are being prepared now for this result that wouldn’t be there if I hadn’t in some sense laid the groundwork. … I think I’d say I was doing God’s work, if I believed in God.”

Reblogged from Arizona State University weh site.

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