Multi Messenger Astronomy...

Figure 1: On 17 August 2017 LIGO detected gravitational waves from a neutron-star collision. Within 12 hours observatories had identified the source of the event GW170817 within the galaxy NGC 4993 – shown in this Hubble Space Telescope image – and located the associated radioactive emissions, or “kilonova”. Hubble observed that flare of light fade over the course of six days, as shown in these observations taken on 22, 26 and 28 August (insets). (Courtesy: NASA, ESA; A Levan (University of Warwick), N Tanvir (University of Leicester), A Fruchter and O Fox (STScI))

Topics: Astronomy, Astrophysics, General Relativity, Gravitational Waves, LIGO, Neutron Stars

04 Jan 2018

Congratulations to Imre Bartos, whose article "A new cosmic messenger" has been picked as one of Physics World's five favourite features of 2018. Taken from the January 2018 issue of Physics World. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

The first observation of gravitational waves from two merging neutron stars that was recently made by the LIGO and Virgo detectors has – along with data from telescopes across the globe and in space – kicked off a new era in multimessenger astronomy. Imre Bartos describes this watershed moment, which crowned decades of research and will shape the future of observational astronomy.

It was almost over. There was only one week to go before the Advanced LIGO and Virgo detectors would complete their observational run, and be shutdown for a year. Indeed, many of my colleagues from the LIGO–Virgo team were already on vacation, while I was awaiting relatives who were visiting. Then my phone buzzed. An automated text message, which read “ALERT FROM GWHEN | New event: G298048 | Check your email!” prompted me to rush to my computer, to look at the signal in a LIGO database. When a flurry of agitated phone calls from collaborators followed, it became clear that a historic moment was unfolding. We observational astronomers needed to act quickly, and as our findings were still a secret, I couldn’t even tell my relatives, who had arrived in the middle of the excitement, why I would need to work.

On 17 August 2017 the LIGO detectors in Louisiana and Washington detected gravitational waves from the collision of two neutron stars – ultracompact dead stars that weigh as much as our Sun, but are barely 20 km in diameter, roughly the size of Manhattan. Such an event had been anticipated for decades, but had never been observed until now. Within two seconds of the arrival of gravitational waves at LIGO, NASA’s Fermi Gamma-ray Space Telescope detected a short gamma-ray burst. This made it even clearer: the gravitational-wave detection – dubbed GW170817 – was not a false alarm, and observatories across the globe quickly needed to turn towards the direction of the collision, or the data would be lost forever. More than 70 telescopes and observatories around the globe and in space were rapidly notified, and were able to execute a co-ordinated survey of the merger and its aftermath, across the full electromagnetic spectrum – gamma-rays, X-rays, light, radio waves – and neutrinos. A new era in multimessenger astronomy had begun (figure 1).

What did we learn?

Neutron-star mergers may be the main source of heavy elements in the universe.

The expansion of the universe can be measured by neutron-star mergers,

We have a new upper limit on the mass of neutron stars.

The neutron stars in GW170817 orbited each other for billions of years before colliding.

The colliding neutron stars created a gamma-ray burst.

There’s something strange about the energetic jet.

A New Cosmic Messenger, Imre Bartos, Physics World
Imre Bartos is an assistant professor at the University of Florida in the US, where he studies extreme cosmic explosions related to the formation and evolution of black holes. He is a member of the LIGO Scientific Collaboration and an associate member of the IceCube Collaboration

Measuring Cosmic Distances...

Image Source: Link below

Topics: Astrophysics, Black Holes, Cosmology, Gravitational Waves, LIGO

Decades of experimental effort paid off spectacularly on 14 September 2015, when the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) spotted the gravitational waves generated by a pair of coalescing black holes.¹ To get a sense of the effort leading to that breakthrough, consider that the gravitational waves caused the mirrors at the ends of each interferometer’s 4 km arms to oscillate with an amplitude of about 10⁻¹⁸ m, roughly a factor of a thousand smaller than the classical proton radius. The detection was also a triumph for theory. The frequency and amplitude evolution of the measured waves precisely matched general relativity’s predictions for the signal produced by a binary black hole merger, even though the system’s gravity was orders of magnitude stronger than that of any system that had been precisely probed before that detection.

Labeled GW150914, that first reported event was soon joined by other detections of binary black hole mergers. Each of those events appeared to be totally dark to traditional astronomical instruments—the matter and electromagnetic fields near the merging black holes were not sufficient to generate any signal other than gravitational. As had long been promised, gravitational waves have opened a window onto an otherwise invisible sector of the universe.

Measuring cosmic distances with standard sirens, Physics Today
Daniel Holz is a professor of physics and of astronomy and astrophysics at the University of Chicago.
Scott Hughes is a professor of physics at MIT in Cambridge, Massachusetts.
Bernard Schutz is a professor of physics and astronomy at Cardiff University in the UK.