How fast is the expansion of the universe? Measuring Cosmic Expansion with Radio Astronomy and Gravitational Waves


Artist’s impression of the explosion and burst of gravitational waves when a pair of superdense neutron stars collide. New observations with radio telescopes suggest that such events can be used to measure the expansion rate of the universe. Sincerely: NRAO / AUI / NSF

How fast is the universe expanding? we are not sure.

Astronomers studied cosmic expansion by measuring the Hubble constant. They have measured this constant in many different ways, but some of their results do not agree with each other. This disagreement, or Tension, There is a growing controversy in astronomy in the Hubble constant. But new observations of neutron stars colliding may provide a solution.

Join Melissa Hoffman, our host of the National Radio Astronomy Observatory as she points out that astronomers and radio astronomers Gravitational waves To answer this cosmic mystery.

Astronomers using National Science Foundation (NSF) radio telescopes have demonstrated how theoretical modeling, as well as a combination of gravitational-wave and radio observations, can transform the merger of pairs of neutron stars into “cosmic rulers”. Which is capable of measuring the extent of expansion. Solving an excellent question on the universe and its rate.

Astronomers study the NSF’s Very Long Baseline Array (VLBA), Carl G., for the subsequent study of the collision of two neutron stars producing gravity. Janski Very Large Array (VLA) and Robert C. Used the Bird Green Bank Telescope (GBT). Waves were detected in 2017. This phenomenon introduced a new way to measure the expansion rate of the universe, known by scientists as Hubble Constant. The expansion rate of the Universe can be used to determine its size and age, as well as an essential tool for interpreting observations of objects elsewhere in the Universe.

Orbital plane orientation

The radio observations of the jet of extruded material in the aftermath of the neutron – star merger were important to allow astronomers to determine the orientation of the orbital plane of stars before their merger, and in this way the “brightness” of the emitted gravitational waves. . Direction of the earth. This can make such events an important new tool for measuring the expansion rate of the universe. Credit: Sophia Dagnello, NRAO / AUI / NSF

Two major methods of determining the Hubble constant are cosmic microwave backgrounds, using the characteristics of leftover radiation big BangOr a specific type of supernova explosion, called Type Ia in the distant universe. However, these two methods give different results.

neutron star The merger gives us a new way to measure the Hubble Constant, and hopes to solve the problem, ”said Kunal Mole of the National Radio Astronomy Observatory (NRAO) and Caltech.

The technique is similar to using supernova explosions. Type Ia supernova explosions are thought to all have an intrinsic glow that can be calculated based on the speed at which they glow and then fade away. Measuring the radiance seen from Earth then tells the distance of the supernova explosion. Measuring the Doppler shift of light from a supernova’s host galaxy indicates the speed at which the galaxy is recirculating from Earth. The speed divided by the distance leaves Hubble Constant. To obtain an accurate figure, many such measurements must be made at different distances.

When two large neutron stars collide, they form an explosion and gravitational waves. The shape of the gravitational-wave signal tells scientists how the bursting of gravitational waves is “bright”. “Glare,” or measuring the intensity of gravitational waves as one can find the distance obtained on Earth.

“This is a completely independent means of measurement that we hope is the true value of the Hubble Constant,” said Moily.

However, there is a twist. The intensity of gravitational waves varies with respect to the orbital plane of two neutron stars with their orientation. Gravitational waves are stronger in the vertical direction of the orbital plane, and are the edge of the orbital plane if viewed from the Earth.

“To use gravitational waves to measure distance, we needed to know that orientation,” said Adam Deller of Swinburne University of Technology in Australia.

Over a period of months, astronomers used radio telescopes to measure the speed of superfast jets of material ejected from the explosion. “We used these measurements with detailed hydrodynamic simulations to determine the orientation angle from which gravitational waves can be used,” said Ehud Nakar of Tel Aviv University.

This single measurement is not yet sufficient for an event 130 million light-years from Earth, scientists said, but the technique now applied to future neutron-star mergers detected with gravitational waves can be done.

“We think 15 more events that can be seen in great detail with gravitational waves and radio telescopes may be able to solve the problem,” said Kenta Hotokazka Princeton University. “This will be an important advance in our understanding of one of the most important aspects of the Universe,” he said.

The international scientific team led by Hotokezaka are reporting their results in the journal Nature astronomy.

References: “Hotblueska, E. Nakar, O. Gottlieb, S. Nissanke, K. Masudan, G. Massinan, K.P. Moileni, and A.T. Deller, on 8 July 2019” in GW170817 from a superluminal motion of jet to a static of jet Measurement “., Nature astronomy.
DOI: 10.1038 / s41550-019-0820-1

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