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Severe neutron-black hole collisions may help settle disputes over cosmic expansion

Neutron star black hole

The intense collision study of black holes and neutron stars could yield new measurements of the cosmic expansion rate, helping resolve a long-standing dispute, suggesting a new model-led study by researchers. 6 minutes from University College London

Our current two best methods of estimating the expansion rate of the universe ̵

1; measuring the brightness and speed of the stellar pulsations and explosions, and looking at the fluctuations in the early cosmic radiation – provide the answer. That’s very different, suggesting that our cosmic theory could be wrong.

The third measure looks at light bursts and ripples in the fabric of space caused by Black holeNeutron star Collisions should help resolve this conflict and clarify whether our cosmic theory needs rewriting.

The new study is published in Physical review letterA simulated scenario of 25,000 black holes and neutron stars colliding with the goal of seeing how much instruments on Earth will detect in mid to late 2020.

Black holes devour neutron stars

A still from NASA animation of a black hole devouring neutron stars.credit: Dana Berry / NASA.

The researchers found that by 2030, instruments on Earth were able to recognize as many as 3,000 ripples in deep space caused by collisions, and for about 100 of these events, the telescope would also see light bursts.

They concluded that this would be enough information to provide a completely independent, accurate and reliable enough measurement of the expansion of the new universe to confirm or deny the need for new physics.

“Neutron stars are dead stars, created when very large stars explode and collapse and become incredibly dense,” said lead author Stephen Feeney (UCL Physics & Astronomy). 10 miles away, but with a massive mass. Twice as much as our sun Collisions with black holes are catastrophic events, causing the so-called spatial ripple. Gravitational wavesWhich we can now detect on Earth with observatories such as LIGO And Virgo

“We haven’t detected the light from these collisions yet. But advances in the sensitivity of gravitational-wave-sensing devices in conjunction with new detectors in India and Japan will lead to a huge leap in terms of the number of these types of events we can detect. It is unbelievably exciting and likely to launch a new era of astrophysics. ”

To calculate the rate of expansion of the universe, known as the Hubble constant, astrophysicists need to know the distance of the astronomical object from the Earth, as well as the speed at which it travels away. Analysis of gravitational waves tells us how far away the collision is, with only the speed left to be determined.

To find out how fast colliding galaxies are moving out, we’ll look at The “red shift” of light, that is, how the wavelength of light from a source is stretched by its motion. The bursts of light that may be accompanied by these collisions will help us identify galaxies in which collisions, allowing researchers to combine distance measurements and red shift measurements in that galaxy.

Dr Feeney said: “The computer model of these cataclysmic events is not complete and this study should provide additional incentives for improvement. If our hypothesis is correct, these large collisions would not cause any detonation we could detect – black holes would devour the star with no trace. But in some cases, smaller black holes may tear neutron stars apart before they swallow them, and may leave matter outside the holes that emit electromagnetic radiation. ”

Co-author Professor Hiranya Piaris (UCL Physics & Astronomy and Stockholm University) said: “Disagreement with the Hubble constant is one of the greatest mysteries in cosmology. In addition to helping to solve this mystery, space time ripples from these catastrophic events, opening up new windows on the universe. We can look forward to many exciting discoveries in the next decade. ”

Gravitational waves were detected at two observatories in the United States (LIGO Labs), one in Italy (Virgo) and another in Japan (KAGRA). The fifth observatory, LIGO-India, is under construction.

Our two best current estimates of cosmic expansion are 67 kilometers per second per megahertz (3.26 million light years) and 74 kilometers per second per megapixel. The first is obtained by analyzing the cosmic microwave background. Big BangOn the other hand, the second comes from comparing stars at different distances from Earth, specifically Cepheids, which exhibit variable luminosity and stellar explosions known as Type Ia supernovas.

Dr Feeney explains: “ As a measure of the microwave background, a complete theory of the universe is needed to be built. But the stellar approach is not, such a conflict presents tantalizing evidence of new physics beyond our current understanding. However, before we can make such claims, we need confirmation of disagreement from observations that are completely independent – we believe these can be obtained from the collision of the black hole’s neutron star. ”

Reference: “The Future for Measuring Hubble’s Constant with Neutron-Star-Black Hole” by Stephen M. Feeney, Hiranya V. Peiris, Samaya M. Nissanke and Daniel J. Mortlock, 28 April 2021, Physical review letter.
DOI: 10.1103 / PhysRevLett.126.171102

The study was conducted by researchers at UCL. Imperial College London, University of Stockholm and the University of Amsterdam It is supported by the Royal Society, the Swedish Research Council (VR), the Knut Foundation and Alice Wallenberg and the Netherlands Organization for Scientific Research (NWO).

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