- 3714 - HUBBLE - measures the universe expansion? The Hubble Space Telescope is still up there working. Although the new James Webb Telescope is getting most of today’s notoriety. Astronomers using the Hubble Space Telescope have made a unique measurement that indicates a jet, plowing through space at speeds greater than 99.97% the speed of light, was propelled by the titanic collision between two neutron stars.
--------------------- 3714 - HUBBLE - measures the universe expansion?
- This explosive event, “GW170817“, was observed in August, 2017. The blast released the energy comparable to that of a supernova explosion. It was the first combined detection of gravitational waves and gamma radiation from a binary neutron star merger.
-
- Two neutron stars, the surviving cores of massive stars that exploded, collided sending a ripple through the fabric of time and space in a phenomenon called “gravitational waves“. A blowtorch jet of radiation was ejected at nearly the speed of light, slamming into material surrounding the obliterated pair. Astronomers used Hubble to measure the motion of a blob of material the jet slammed into.
-
- The aftermath of this merger was collectively seen by 70 observatories around the globe and in space, across a broad swath of the electromagnetic spectrum in addition to the gravitational wave detection. Thus heralding a significant breakthrough for the emerging field of “Time Domain and Multi-Messenger Astrophysics“, the use of multiple "messengers" like light and gravitational waves to study the universe as it changes over time.
-
- 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 jets moving outward from its poles. The roaring jet smashed into and swept up material in the expanding shell of explosion debris. This included a blob of material through which a jet emerged.
-
- The Hubble observation was combined with observations from multiple National Science Foundation radio telescopes working together for “very long baseline interferometry” (VLBI). The radio data were taken 75 days and 230 days after the explosion.
-
- The smashup between these two dense stellar remnants unleashes the energy of 1,000 standard stellar nova explosions. In the aftermath of the collision a blowtorch jet of radiation is ejected at nearly the speed of light. The jet is directed along a narrow beam confined by powerful magnetic fields. The roaring jet plowed into and swept up material in the surrounding interstellar medium.
-
- By combining the different observations, astronomers were able to pinpoint the explosion site. The Hubble measurement showed the jet was moving at an apparent “velocity of seven times the speed of light“. The radio observations show the jet later had decelerated to an apparent speed of four times faster than the speed of light.
-
- In reality, nothing can exceed the speed of light, so this "superluminal" motion is an illusion. Because the jet is approaching Earth at nearly the speed of light, the light it emits at a later time has a shorter distance to go. In essence the jet is chasing its own light. In actuality more time has passed between the jet's emission of the light than the observer thinks. This causes the object's velocity to be overestimated, in this case seemingly exceeding the speed of light.
-
- Further analysis indicates that the jet was moving at least at 99.97% the speed of light when it was launched.
-
- The Hubble measurements, combined with the VLBI measurements greatly strengthen the long-presumed connection between neutron star mergers and short-duration gamma-ray bursts. That connection requires a fast-moving jet to emerge, which has now been measured in GW170817.
-
- This work paves the way for more precision studies of neutron star mergers, detected by the LIGO, Virgo, and KAGRA gravitational wave observatories. With a large enough sample over the coming years, relativistic jet observations might provide another line of inquiry into measuring the universe's expansion rate, associated with a number known as the Hubble constant of the universe expansion rate.
-
- At present there is a discrepancy between Hubble constant values as estimated for the early universe and nearby universe. The differing values are based on extremely precise measurements of Type 1a supernovae by Hubble and other observatories, and Cosmic Microwave Background measurements by ESA's Planck satellite. More science is needed to reconcile these differences.
-
October 19, 2022 HUBBLE - measures the universe expansion? 3714
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Sunday, October 23, 2022 ---------------------------
No comments:
Post a Comment