Home / Science / Neutron-black-hole collisions can eventually end to end different measurements in the rate of cosmic expansion.

Neutron-black-hole collisions can eventually end to end different measurements in the rate of cosmic expansion.



If you’ve been following the development of astronomy over the past few years, you may have heard of the so-called. This “cosmological crisis” leaves astronomers wondering if there may be something wrong with our current understanding of the universe. This crisis revolves around the rate at which the universe expands: The current cosmic expansion rate is inconsistent with the early measurements of the expansion rate in the universe. With no indication of why these measurements were disagreed, astronomers lost to account of the inequality.

The first step in solving this puzzle is to try a new method of measuring expansion. In a paper published last week, researchers from University College London (UCL) point out that we can create new and independent measurements of the expansion of the universe by observing the collisions of black hole stars with Neutron star

Let’s back up for a moment and talk where things are right now. When we look out into the universe, distant galaxies appear to be moving further away from us than closer galaxies as space is expanding. This is represented by a number called the Hubble constant, often written as velocity. (In kilometers per second) of galaxies one megapixel away (Mpc).

One of the best ways to measure Hubble’s constant is to observe objects known as cepheid variables.Cepheids are regular bright and dim stars, and their luminosity arises to match. Their time (Time it takes to dim and light up again) The consistency of these objects makes it possible to estimate distances, and many Cepheids surveys give us a Hubble constant of about 73 km / s / Mpc. Type 1A supernova is another common object with known brightness and still provides Hubble constant around 73 km / s / Mpc.

On the other hand, you can measure the early expansion of the universe by observing the Big Bang’s rays, also known as Cosmic Microwave Background Radiation (CMB) .Our best CMB measurement was taken. By the European Space Agency’s Planck spacecraft, which released its final data in 2018, Planck observed a Hubble constant of 67.66 km.

Approximate value of the Hubble constant Black represents measurements from Cepheids / Type 1A Supernovae (73 km / s / Mpc). Red represents CMB measurements of early cosmos (67 km / s / Mpc). Blue shows other techniques which are uncertain. It’s not small enough to decide between the two.Credit: Renerpho (Wikimedia Commons).

The difference between 67 and 73 isn’t huge, and at first the most plausible explanation for the difference appears to be a tool bug. However, based on later observations, the error bars in these measurements were narrowed enough to make the differences statistically significant. Crisis, of course!

This is where UCL researchers hope to step in.They propose a new method for measuring the Hubble constant, which does not rely on any of the other two methods. It starts with measuring gravitational waves: ripples in spacetime that are caused by collisions of large objects such as black holes. Gravitational waves were first detected as recently as 2015 and are not yet involved in a visible collision.

As Lead Researcher Stephen Feeney explains, “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 events of this kind that we can detect. ”

Gravitational waves help us determine the location of these collisions. But we also need to measure the light from the collision if we want to measure its speed. A black hole’s neutron star collision may be the only type of event that produces both.

If we see enough of these collisions, we can use them to create a new measure for the Hubble constant.

LIGO Gravitational Wave Detector in Louisiana Image credit: Caltech / MIT / LIGO Laboratory.

The UCL team used simulations to estimate the number of neutron-black hole collisions that could occur over the next decade. They found that the Earth’s gravitational wave detectors may have picked up 3000 pieces before 2030, and about 100 of them might produce visible light.

Just that is enough For this reason, by 2030 we may have the latest in measurements of the Hubble constant. We do not yet know whether the new measurements will either agree with the CMB measurement or with the Cepheid / Type 1A measurement, or both. But the outcome, whatever it may be, will be a huge step forward in solving the puzzle. It could calm the crisis in cosmology or make it more serious, forcing us to take a closer look at our cosmic model and admit that there is something we don’t know about the universe more than we think.

Learn more: “Black-neutron star collisions may settle disputes about cosmic expansion.” UCL.

Stephen M. Feeney, Hiranya V. Peiris, Samaya M. Nissanke and Daniel J. Mortlock “Opportunities for Measuring Hubble’s Constants by Neutron-Star-Black Hole Combination.” Physical review letter

Featured image: Black hole devouring neutron stars.credit: Dana Berry / NASA.


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