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New research suggests innovative method to analyse the densest star systems in the Universe

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New research suggests innovative method to analyse the densest star systems in the Universe
Artist’s illustration of supernova remnant Credit: Pixabay

In a recently published study, a team of researchers led by the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at Monash university suggests an innovative method to analyse gravitational waves from neutron star mergers, where two stars are distinguished by type (rather than mass), depending on how fast they’re spinning.


Neutron stars are extremely dense stellar objects that form when giant stars explode and die—in the explosion, their cores collapse, and the protons and electrons melt into each other to form a remnant neutron star.

In 2017, the merging of two neutron stars, called GW170817, was first observed by the LIGO and Virgo gravitational-wave detectors. This merger is well-known because scientists were also able to see light produced from it: high-energy gamma rays, visible light, and microwaves. Since then, an average of three scientific studies on GW170817 have been published every day.

In January this year, the LIGO and Virgo collaborations announced a second neutron star merger event called GW190425. Although no light was detected, this event is particularly intriguing because the two merging neutron stars are significantly heavier than GW170817, as well as previously known double neutron stars in the Milky Way.

Scientists use gravitational-wave signals—ripples in the fabric of space and time—to detect pairs of neutron stars and measure their masses. The heavier neutron star of the pair is called the ‘primary’; the lighter one is ‘secondary’.

The recycled-slow labelling scheme of a binary neutron star system

A binary neutron star system usually starts with two ordinary stars, each around ten to twenty times more massive than the Sun. When these massive stars age and run out of ‘fuel’, their lives end in supernova explosions that leave behind compact remnants, or neutron stars. Each remnant neutron star weighs around

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A mini fractal universe may lie inside charged black holes (if they exist)

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Black holes are perhaps the strangest, least-understood objects in our universe. With so much potential — being linked to everything from wormholes to new baby universes — they have sucked in physicists for decades. 

But as strange as these known objects are, even stranger types of black holes could be dreamed up. In one upside-down, hypothetical version of the universe, a bizarre type of black hole could exist that is stranger than an M.C. Escher sketch. Now, a team of researchers has plunged into the mathematical heart of so-called charged black holes and found a slew of surprises, including an inferno of space-time and an exotic fractal landscape … and potentially more.

Related: 9 ideas about black holes that will blow your mind

Welcome to a holographic superconductor

There are all sorts of potential, hypothetical black holes: ones with or without electric charge, ones spinning or stationary, ones surrounded by matter or those floating in empty space. Some of these hypothetical black holes are known for certain to exist in our universe; for example, the rotating black hole surrounded by infalling matter is a pretty common presence. We’ve even taken a picture of one.

But some other kinds of black holes are purely theoretical. Even so, physicists are still interested in exploring them — by diving into their mathematical foundations, we can realize new relationships and implications of our physical theories, which can have real-world consequences. 

One such theoretical black hole is an electrically charged black hole surrounded by a certain kind of space known as anti-de Sitter. Without getting into too much of the nitty-gritty, this kind of space has constant negative geometric curvature, like a horse saddle, which we know is not a good description of our universe. (A cosmos with anti-de Sitter space, all else being

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Physicists Calculate Upper Limit For Speed Of Sound In The Universe

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KEY POINTS

  • Physicists tested sound as it travels through different materials
  • Sound can almost reach its upper limit when traveling in solid atomic hydrogen
  • The finding is vital in different fields of studies like materials science and condensed matter physics

Sound waves can travel to up to 36 kilometers or more than 22 miles per second when traveling through solids or liquids, a new study by a team of physicists revealed. The physicists said that their calculation could be the first known variables representing the threshold of sound waves.    

Before this new finding, the speed of sound was measured based on Albert Einstein’s theory of special relativity that identified sound waves threshold similar to that of the speed of light (300,000 kilometers or over 186,000 miles per second).

In a study, published in the journal Science Advances, the physicists said to calculate for the threshold of the speed of sound, they factored in the two dimensionless fundamental constants. These constants are the fine structure constant and the proton-to-electron mass ratio. 

The physicists explained that these two fundamental constants have already been used in calculations needed to understand the Universe. For instance, the dimensionless fundamental constants are also the basis for calculations of nuclear reactions, proton decay, and nucleosynthesis in stars. The balance between the fundamental constants could also point to the habitable zone where possible life forms could start outside Earth. 

With identifying the upper limit of sound, their finding also became significant in other fields of studies. Setting a known upper threshold of sound is particularly crucial to studies that test the limits of matter such as materials science and condensed matter physics.      

“We believe the findings of this study could have further scientific applications by helping us to find and understand limits of different properties such as viscosity

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Astrophysicists figure out the total amount of matter in the universe

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The stuff that makes up our universe is tricky to measure, to put it mildly. We know that most of the universe’s matter-energy density consists of dark energy, the mysterious unknown force that’s driving the universe’s expansion. And we know that the rest is matter, both normal and dark.

Accurately figuring out the proportions of these three is a challenge, but researchers now say they’ve performed one of the most precise measurements yet to determine the proportion of matter.

According to their calculations, normal matter and dark matter combined make up 31.5 percent of the matter-energy density of the universe. The remaining 68.5 percent is dark energy.

“To put that amount of matter in context, if all the matter in the universe were spread out evenly across space, it would correspond to an average mass density equal to only about six hydrogen atoms per cubic meter,” said astronomer Mohamed Abdullah of the University of California, Riverside and the National Research Institute of Astronomy and Geophysics in Egypt.

“However, since we know 80 percent of matter is actually dark matter, in reality, most of this matter consists not of hydrogen atoms but rather of a type of matter which cosmologists don’t yet understand.”

Understanding dark energy is actually crucial to our understanding of the Universe. We don’t know what it is, exactly – the ‘dark’ in the name refers to that mystery – but it appears to be the force that drives the expansion of the Universe, the velocity of which has proven incredibly difficult to narrow down past a certain point.

Once we have a better understanding of the expansion rate, that will improve our grasp of the evolution of the Universe as a whole. Hence, constraining the properties of dark energy is a pretty important undertaking for cosmology in

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What’s The Matter With The Universe? Scientists Have The Answer

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A team of US astrophysicists has produced one of the most precise measurements ever made of the total amount of matter in the Universe, a longtime mystery of the cosmos.

The answer, published in The Astrophysical Journal on Monday, is that matter consists of 31.5 percent — give or take 1.3 percent — of the total amount of matter and energy that make up the Universe.

The remaining 68.5 percent is dark energy, a mysterious force that is causing the expansion of the Universe to accelerate over time, and was first inferred by observations of distant supernovae in the late 1990s.

Put another way, this means the total amount of matter in the observable Universe is equivalent to 66 billion trillion times the mass of our Sun, Mohamed Abdullah, a University of California, Riverside astrophysicist and the paper’s lead author told AFP.

Most of this matter — 80 percent — is called dark matter. Its nature is not yet known but it may consist of some as-yet-undiscovered subatomic particle.

The latest measurements correspond well with values previously found by other teams using different cosmological techniques, such as by measuring temperature fluctuations in the low-energy radiation left over from the Big Bang.

“This has been a long process over the course of 100 years where we’re gradually getting more and more precise,” Gillian Wilson, the study’s co-author and a professor at UCR told AFP.

“It’s just kind of cool to be able to make such a fundamental measurement about the Universe without leaving planet Earth,” she added.

So how exactly do you weigh the Universe?

The team honed a 90-year-old technique that involves observing how galaxies orbit inside galaxy clusters — massive systems that contain thousands of galaxies.

These observations told them how strong each galaxy cluster’s gravitational pull was, from

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