Laser Interferometer Gravitational-wave Observatory (LIGO) was taken offline in 2018 so that upgrades could be made to its instruments. Upgrades made to both LIGO and Virgo have increased the sensitivity of its instruments by about 40%.
This would allow detections to take place weekly or more often. After completing the upgrades on April 1st 2019, the observatory detected two probable GW (gravitational wave) events in the space of two weeks.
These two new GW events occurred on April 8th and April 12th, 2019. The signals, are believed to have been the result of a pair of black holes merging, was detected thanks to the three-facility collaboration between LIGO and the Virgo Observatory in Italy.
A team of scientists from Penn State University, led by Chad Hanna, an associate Professor of physics, astronomy and astrophysics, played a vital role in these latest detections.
LIGO public alert system – Where, when and What of GW’s
They have also implemented a public alert system as part of their third observation run. LIGO public alerts also include a sky-map that shows:
- The possible location of the source in the sky
- The time of the event
- What kind of event it is believed to be
LIGO has also said that in the future, announcements of candidate events will be followed by more detailed information once they have had a chance to properly vet and study them.
In this iteration, the LIGO team sends out alerts the moment detection are made to the astronomical community. In seconds, the observatories around the world can point their telescopes at the source, observing the source in different wavelengths (optical, X-ray, ultraviolet, radio, etc.).
This allows scientists hope to learn more about what causes GW events and about the dynamics behind them.
Penn State and LIGO – Team behind Real-time data on GW candidates
LIGO became famous in February of 2016 when scientists announced the first-ever detection of gravitational waves. These events provide insight into cosmic phenomena predicted over a century ago by Einstein’s Theory of General Relativity.
Penn State University leads the astronomy community in collecting and analyzing the data in real time. As Cody Messick, a graduate student in physics at Penn State and member of the LIGO team, explained: “Penn State is part of a small team of LIGO scientists that analyze the data in almost real-time. We are constantly comparing the data to hundreds of thousands of different possible gravitational waves and upload any significant candidates to a database as soon as possible. Although there are several different teams all performing similar analyses, the analysis ran by the Penn State team uploaded the candidates that were made public for both of these detections.”
Messick has been responsible for ensuring that newly-uploaded GW candidates contain information from all detectors for the past 9 months. With all the detectors running all the time, astronomers can use the uploaded data to localize signals by narrowing down the predicted area of the sky that the signal is coming from.
As Ryan Magee, a graduate student in physics at Penn State and member of the LIGO team, put it: “These are near real-time detections of gravitational waves produced from two probable black holes colliding. We detected the first signal within about 20 seconds of its arrival to earth. We can set up automatic alerts to get phone calls and texts when a significant candidate is identified. I thought I was getting a spam phone call at first!”
LIGO and the future – Black holes and Neutron Star Detection
So far, astronomers have deduced that GW events can be the result of:
- Binary black hole mergers
- A merger between a black hole and a neutron star
- Binary neutron star merger
Each of these events produces gravitational waves with very different signals. This allows astronomers to determine the cause. In this case, the events are believed to be the result of binary black hole mergers. Follow-up observations in the coming weeks and months will verify this.
Surabhi Sachdev, an Eberly Postdoctoral Research Fellow in physics at Penn State and member of the LIGO team, explained the importance of these latest events: “This is the first LIGO observation that was made public right away in an automated fashion. This is the new LIGO policy starting with this observing run. Events are instantly made public automatically. After human vetting, a confirmation or retraction is issued within hours.”
With the increased sensitivity of their detectors, the LIGO team hopes to:
- Make more detections
- Detect a greater variety of signals
So far, events have been detected that were the result of mergers between:
- Two black holes
- Two neutron stars
In the near future, the team might detect a signal produced by the merger of a black hole and a neutron star. The public can keep track of public alerts at https://gracedb.ligo.org/latest/, or you can download the alert app at Gravitational Wave Events iPhone App.
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