Two neutron stars have a "close encounter". Is the jet close to the speed of light a blessing or a curse?

Hubble shows neutron star collision jets travel at nearly the speed of light

In August 2017, astronomers observed a rare explosion when two ultra-compact neutron stars collided head-on, releasing an extremely powerful jet of radiation.

Two days later, Hubble began observing the jet. Astronomers detected gravitational waves from a neutron star for the first time during that explosion. Now, five years later, scientists have finally been able to measure the speed of that radiation stream.

"The results show that the speed of the jet at the beginning of launch was 99.97% of the speed of light," said Wenbin Lu from the University of California, Berkeley, who was responsible for data interpretation, in a report.

An artist's illustration of a neutron star collision. (Image credit: Elizabeth Wheatley (STScI))

An artist's interpretation of a collision between two neutron stars. (Image credit: Elizabeth Wheatley (STScI))

Scientists called the event GW170817, and it was initially detected through gravitational waves and gamma rays produced by the explosion. These signals were captured by 70 observatories in Earth and near-Earth orbit, including Hubble. The data showed that the collision of these ultra-compact neutron stars was enough to create a black hole and an explosion with a total energy release comparable to a supernova.

As the newborn black hole grows, it begins to draw surrounding matter into a vortex disk, which then ejects matter from the center in two directions - this is the cause of the jets observed by Hubble.

To calculate the speed of the jet, scientists specifically observed the movement of a small group of explosion debris, which was carried into space by the jet. "The determination of the trajectory of the debris requires extremely high data accuracy, equivalent to measuring the diameter of a 12-inch pizza on the moon from Earth. These high-precision data were collected by Hubble and some radio telescopes," NASA officials wrote in a report.

This is difficult because the jet is coming directly at Earth, which makes it appear to be traveling much faster than the speed of light, which is 4 or 7 times faster than light.

"I was surprised at how accurate the Hubble measurements were, even comparable to the powerful Very Long Baseline Interferometry radio telescopes that are spread all over the world," said Kunal P. Murray of Caltech, lead author of a new paper on the research.

It took scientists five years to find a method powerful enough to analyze the event. It was a long time, but it was worth it. Now scientists have more methods to choose from to analyze the merger of neutron stars. More specifically, they can further study gravitational waves, which will help to accurately measure the expansion rate of the universe in the future.

Muhly's paper was successfully published in the journal Nature on Wednesday (October 13).

Related knowledge

A neutron star is the collapsed core of a supergiant star. Supergiants have masses between 10 and 25 times that of our sun, and can be much more if they are rich in metals. Aside from black holes and some hypothetical objects such as white holes, quark stars, and strange stars, neutron stars are the smallest and densest class of objects known. A neutron star has a radius of about 10 kilometers (6 miles) and can weigh up to 1.4 times the mass of our sun. They form when a giant star explodes as a supernova, accompanied by gravitational collapse. In this process, the core of the star is compressed, and its density exceeds that of a white dwarf, eventually reaching the density of an atomic nucleus.

The Hubble Space Telescope is a space telescope that was launched into low-Earth orbit in 1990 and is still in operation. Hubble was not the first space telescope, but it is one of the largest and most versatile, making it a powerful scientific tool and a astronomical blessing for the general public. The Hubble Space Telescope is a major NASA observatory named after astronomer Edwin Hubble. The Space Telescope Science Institute selects Hubble's observation objects and processes the collected data, while the Godard Space Flight Center operates the space shuttle.

A black hole is a quasar that is like an ideal black body. It does not reflect light[6][7] and has such a strong gravitational pull that it forms a region from which all particles and electromagnetic radiation, such as light, cannot escape[8].

General relativity predicts that sufficiently compact masses can warp spacetime to form a black hole[9][10]; the boundary of the region beyond which escape is impossible is called the event horizon. Although the event horizon has a profound effect on the fate and behavior of objects that cross it, observations of the region do not appear to detect any signatures.[11] Furthermore, quantum field theory in curved spacetime predicts that the event horizon emits Hawking radiation, which, like the spectrum of a black body, can be used to measure a temperature inversely proportional to its mass. For black holes of stellar mass, this temperature is typically on the order of a few billionths of a kelvin and is therefore essentially unobservable.

BY:Stefanie Waldek

FY: taokesasi

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