beecee Posted January 8, 2018 Share Posted January 8, 2018 Gravitational waves measure the universe January 8, 2018, Harvard-Smithsonian Center for Astrophysics NGC4993, the galaxy hosting the gravitational wave event GW170817 that has been used to measure the age of the universe. The source of the event is the red dot to the upper left of the galaxy's center; it was not there in earlier images. Credit: NASA and ESA The direct detection of gravitational waves from at least five sources during the past two years offers spectacular confirmation of Einstein's model of gravity and space-time. Modeling of these events has also provided information on massive star formation, gamma-ray bursts, neutron star characteristics, and (for the first time) verification of theoretical ideas about how the very heavy elements, like gold, are produced. Astronomers have now used a single gravitational wave event (GW170817) to measure the age of the universe. CfA astronomers Peter Blanchard, Tarreneh Eftekhari, Victoria Villar, and Peter Williams were members of a team of 1314 scientists from around the world who contributed to the detection of gravitational waves from a merging pair of binary neutron stars, followed by the detection of gamma-rays, and then the identification of the origin of the cataclysm in a source in the galaxy NGC4993 spotted in images taken with various time delays at wavelengths from the X-ray to the radio.An analysis of the gravitational waves from this event infers their intrinsic strength. The observed strength is less, implying (because the strength diminishes with distance from the source) that the source is about 140 million light-years away. NGC4993, its host galaxy, has an outward velocity due to the expansion of the universe that can be measured from its spectral lines. Knowing how far away it is and how fast the galaxy is moving from us allows scientists to calculate the time since the expansion began – the age of the universe: between about 11.9 and 15.7 billion years given the experimental uncertainties. Read more at: https://phys.org/news/2018-01-gravitational-universe.html#jCp the paper: https://www.nature.com/nature/journal/v551/n7678/full/nature24471.html A gravitational-wave standard siren measurement of the Hubble constant: On 17 August 2017, the Advanced LIGO1 and Virgo2 detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system3. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source4, 5, 6. This sky region was subsequently observed by optical astronomy facilities7, resulting in the identification8, 9, 10, 11, 12, 13 of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ‘multi-messenger’ astronomical observation. Such observations enable GW170817 to be used as a ‘standard siren’14, 15, 16, 17, 18 (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic ‘distance ladder’19: the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements20, 21, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision. 1 Link to comment Share on other sites More sharing options...
beecee Posted January 9, 2018 Author Share Posted January 9, 2018 Some interesting, if obvious points re the article...... https://phys.org/news/2018-01-gravitational-universe.html "Knowing how far away it is and how fast the galaxy is moving from us allows scientists to calculate the time since the expansion began – the age of the universe: between about 11.9 and 15.7 billion years given the experimental uncertainties". and...... "The age derived from this single event is consistent with estimates from decades of observations relying on statistical methods using two other sources: the cosmic microwave background radiation (CMBR) and the motions of galaxies" "With a large statistical sample of gravitational wave events of all types, the current range of values for the age will narrow". "Although both the CMBR and the galaxy measurements are each quite precise, they seem to disagree with each other at roughly the ten percent level. This disagreement could just be observational error, but some astronomers suspect it might be a real difference reflecting something currently missing from our picture of the cosmic expansion process, perhaps connected with the fact that the CMBR arises from a vastly different epoch of cosmic time than does the galaxy data. This third method, gravitational wave events, may help solve the puzzle". Link to comment Share on other sites More sharing options...
Silvestru Posted January 10, 2018 Share Posted January 10, 2018 Really interesting read. Thank you beecee! Link to comment Share on other sites More sharing options...
beecee Posted January 10, 2018 Author Share Posted January 10, 2018 3 hours ago, Silvestru said: Really interesting read. Thank you beecee! No probs...As has been said many times, a whole new region of cosmology opened up for scientists, The mind boggles! Link to comment Share on other sites More sharing options...
interested Posted January 12, 2018 Share Posted January 12, 2018 Is this the same BH that is burping according to the BBC. http://www.bbc.co.uk/news/science-environment-42655685?ocid=global_bbccom_email_12012018_top+news+stories Can BH's eject matter from beyond the event horizon, or do these kind of burps originate in the accretion disc.I included the following link because there are lots of other interesting links at the bottom. https://www.sciencedaily.com/releases/2018/01/180111162934.htm Link to comment Share on other sites More sharing options...
Strange Posted January 12, 2018 Share Posted January 12, 2018 1 hour ago, interested said: Is this the same BH that is burping according to the BBC. No. " the detection of gravitational waves from a merging pair of binary neutron stars" Quote Can BH's eject matter from beyond the event horizon, or do these kind of burps originate in the accretion disc.I included the following link because there are lots of other interesting links at the bottom. You should really start a new thread for new topics, rather than hijacking others (including your own). The "burbs" originate from matter falling into the black hole, in other words the accretion disk. Remember, nothing can come out of the event horizon. That s why it is called an event horizon. Link to comment Share on other sites More sharing options...
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