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Over the weekend, astronomer J. Craig Wheeler of the University of Texas at Austin launched speculation over a potential new LIGO detection by tweeting: “New LIGO. Source with optical counterpart. Blow your sox off!”
By optical counterpart, he probably means that astronomers could observe light emitted by the gravitational wave source. This suggests the source is neutron stars as, unlike black holes, they can be seen in visible wavelengths. LIGO researchers have long-anticipated this possibility, setting up partnerships with optical observatories to rapidly follow-up on potential signals prior to formally announcing a discovery.
LIGO spokesperson David Shoemaker dodged confirming or denying the rumours, saying only “A very exciting O2 Observing run is drawing to a close August 25. We look forward to posting a top-level update at that time.”
Speculation is focused on NGC 4993, a galaxy about 130 million light years away in the Hydra constellation. Within it, a pair of neutron stars are entwined in a deadly dance.
Starting August 17 and continuing every night since, the Visible and Infrared Survey Telescope for Astronomy at Cerro Paranal in Chile has taken survey images intended to spot a kilonova, the proposed observational signature of two colliding neutron stars, based on a LIGO gravitational wave detection. Another instrument on the same mountain took spectra from a part of that region of the sky for over four and a half hours from August 19 to 22.
Current theories suggest they most likely emerged during what researchers call an r-process—as in rapid. As part of the process, large numbers of neutrons would come under high densities, resulting in capture by atomic nuclei—clearly, an extreme environment. The most likely candidate for creating such an environment is a supernova, but there seem to be too few of them to account for the amounts of heavy elements that exist. In this new effort, the researchers offer a new idea. They believe it is possible that PBHs [primordial black holes] occasionally collide with neutron stars, and when that happens, the PBH becomes stuck in the center of the star. Once there, it begins pulling in material from the star's center.
... if a PBH happened to bump into a neutron star, it would take up residence in its center and commence pulling in neutrons and other material. That would cause the star to spin rapidly, which in turn would fling material from its outermost layer into space. The hurled material, the researchers suggest, would be subjected to an environment that would meet the requirements for an r-process, leading to the creation of heavy metals.
originally posted by: verschickter
So in less than two or three years we (or better, science) managed to pick up not only one type of gravity wave but two different ones?
Is that correct?
originally posted by: stormcell
Having a bunch of people who do work in the field all eager over a tweet and sensor logs... well, makes me wonder what is happening!
“New LIGO. Source with optical counterpart. Blow your sox off!” [Tweet that started the furor]
[Craig] Wheeler later apologized on Twitter. “Right or wrong, I should not have sent that tweet. LIGO deserves to announce when they deem appropriate. Mea culpa,” he wrote.
Public records show that NASA’s Fermi Gamma-ray Space Telescope has spotted γ-rays emerging from the same region of sky as the potential gravitational-wave source.
On 22 August, a Twitter feed called Space Telescope Live, which provides live updates of what the Hubble Space Telescope is looking at, suggested that a team of astronomers was looking at a binary neutron-star merger using the probe’s on-board spectrograph, which is what astronomers would normally use to look at the afterglow of a short GRB [gamma ray burst]. The Hubble tweet has since been deleted. Public records also confirm that multiple teams have used the Hubble Space Telescope over the last week to examine NGC 4993, and state as their reason that they are trying to follow up on a candidate observation of gravitational waves.
On 23 August, a commenter on the blog of astrophysicist Peter Coles, of Cardiff University in the UK, noted that NASA’s Chandra X-ray observatory had jumped into the action, too.
Update 25 August: The LIGO–Virgo collaboration posted its top-level update, saying: “Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share.”
In August 2017, astronomers reported that a gamma-ray burst, named GRB 170817A, and a possible gravitational wave, tentatively named GW170818, that may have been emitted in the collision of two neutron stars,
The scenario that emerged is that the initial merger of the two superdense neutron stars caused an explosion that propelled a spherical shell of debris outward. The neutron stars collapsed into a black hole whose powerful gravity began pulling material toward it. That material formed a rapidly-spinning disk that generated a pair of jets moving outward from its poles.
As the event unfolded, the question became whether the jets would break out of the shell of debris from the original explosion. Data from observations indicated that a jet had interacted with the debris, forming a broad "cocoon" of material expanding outward. Such a cocoon would expand more slowly than a jet.
"Our interpretation is that the cocoon dominated the radio emission until about 60 days after the merger, and at later times the emission was jet dominated," said Ore Gottlieb, of the Tel Aviv University, a leading theorist on the study.
"We were lucky to be able to observe this event, because if the jet had been pointed much farther away from Earth, the radio emission would have been too faint for us to detect," said Gregg Hallinan of Caltech.
The detection of a fast-moving jet in GW170817 greatly strengthens the connection between neutron star mergers and short-duration gamma-ray bursts, the scientists said. They added that the jets need to be pointed relatively closely toward the Earth for the gamma ray burst to be detected.
We measured an apparent motion that is four times faster than light. That illusion, called superluminal motion, results when the jet is pointed nearly toward Earth and the material in the jet is moving close to the speed of light.
-Kunal Mooley, National Radio Astronomy Observatory (NRAO) and Caltech.