Tag Archives: astrophysicist

Astrophysicist Unveils Innovative Method for Measuring the Hubble Constant

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Astrophysicists from the University of Illinois and the University of Chicago have pioneered a groundbreaking method to determine the Hubble constant, which quantifies the rate of the universe’s expansion. By utilizing the subtle background sound of gravitational waves, this innovative technique is poised to transform our understanding of cosmic evolution and may resolve key debates in contemporary astrophysics.

Schematic diagram of the universe’s expansion from the Big Bang to the present. Image credit: NASA/EFBrazil.

“This discovery holds significant importance. To address the ongoing Hubble tension, obtaining an independent measurement of the Hubble constant is crucial,” stated Professor Nicolas Younes from the University of Illinois.

“Our approach innovatively leverages gravitational waves to enhance the accuracy of Hubble constant measurements.”

Professor Younes and colleagues introduced a novel gravitational wave method utilizing the faint “background hum” from numerous distant black hole mergers to enhance Hubble constant estimations.

In contrast to traditional measurement techniques, this method capitalizes on space-time distortions, or gravitational waves, which carry valuable insights about vast cosmic distances and the velocity of receding celestial bodies.

Astrophysicists have termed this approach the “stochastic siren” method.

“By observing distinct black hole mergers, we can ascertain the frequency of these events throughout the universe,” remarked Bryce Cousins, a graduate student at the University of Illinois.

“Considering their velocity, we anticipate many additional events occurring that remain undetected, referred to as the gravitational wave background.”

“Discovering a completely new tool for cosmological research is a rare occurrence,” added Daniel Holtz, a professor at the University of Chicago.

“We demonstrated that we can unravel the age and composition of the universe by harnessing the ambient sound of gravitational waves resulting from the merger of black holes across distant galaxies.”

“This is an exhilarating and entirely novel direction, and we eagerly anticipate applying our method to future datasets to assist in determining the Hubble constant and other vital cosmological parameters.”

As the sensitivity of gravitational wave detectors improves, the stochastic siren method could lay the foundation for precision cosmology.

Detection of gravitational wave backgrounds is anticipated within the next six years.

Until then, the method gradually restricts higher Hubble constant values as improved upper background limits emerge, providing additional insights into the Hubble tension even without full detection capabilities.

“This initiative should pave the way for future applications, enhancing our sensitivity and ability to better filter and potentially detect the gravitational wave background,” Cousins noted.

“We hope that incorporating this information will yield superior cosmological insights and bring us closer to resolving the Hubble tension.”

The team’s research will be published in the Physical Review Letters.

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Bryce Cousins et al. 2026. Stochastic Siren: Astrophysical Gravitational Wave Background Measurement of the Hubble Constant. Physics. in press. doi: 10.1103/4lzh-bm7y

Source: www.sci.news

Astrophysicist reveals the genesis of one of the Milky Way’s biggest moons

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Satellite Galaxy Crater II The Milky Way's Crater 2 (or Crater 2) is located in the constellation Crater, about 380,000 light-years from Earth. This galaxy is very cold, very diffuse, and has a low surface brightness. According to a new study, Crater 2 exists thanks to self-interacting dark matter.

Location of Crater II and other Milky Way moons at distances between 100,000 and 400,000 parsecs from the Sun. Image courtesy of Torrealba others., doi: 10.1093/mnras/stw733.

” discovery “Since 2016, there have been numerous attempts to recreate the anomalous properties of Crater II, but these have proven extremely difficult,” said Haibo Yu, a professor at the University of California, Riverside.

Dark matter makes up 85% of the matter in the universe, and under the influence of gravity it can form spherical structures called dark matter halos.

Invisible halos permeate and surround galaxies like Crater II, and the fact that Crater II is so cold indicates that its halo is low density.

“Crater II developed within the Milky Way's tidal field and experienced tidal interactions with its host galaxy, similar to how Earth's oceans experience tidal forces due to the Moon's gravity,” Professor Yu said.

“In theory, tidal interactions can reduce the density of dark matter haloes.”

However, recent measurements of Crater II's orbit around the Milky Way suggest that if dark matter is made of cold, collisionless particles, as predicted by the prevailing cold dark matter theory (CDM), the strength of the tidal interactions is too weak to reduce the dark matter density in the satellite galaxy enough to match the measurements.

“Another mystery is why Crater II is so large when, as the satellite galaxy evolves in the Milky Way's tidal field, tidal interactions should reduce its size,” said Professor Yu.

Professor Yu and his colleagues put forward a different theory to explain the properties and origin of Crater II.

This is called self-interacting dark matter (SIDM) and can plausibly explain the diverse distribution of dark matter.

The theory proposes that dark matter particles self-interact through the dark force and collide with each other forcefully near the center of the galaxy.

“Our study shows that SIDM can explain the anomalous properties of Crater II,” said Professor Yu.

“The key mechanism is that dark matter self-interaction thermalizes Crater II's halo and creates a shallow dense core, i.e. the dark matter density flattens out at a small radius.”

“In contrast, in a CDM halo, the density would increase rapidly towards the center of the galaxy.”

“In SIDM, the strength of the relatively weak tidal interaction, consistent with what is expected from measurements of Crater II's orbit, is sufficient to reduce the dark matter density in Crater II, consistent with observations.”

“Importantly, the size of galaxies is also increasing within the SIDM halo, which could explain the large size of Crater II.”

“Dark matter particles are only more loosely bound in the cored SIDM halo than in the pointed CDM halo.”

“Our study shows that SIDM is a better option than CDM for explaining the origin of Crater II.”

of study Published in Astrophysical Journal Letters.

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Zhang Xingyu others2024. Interpreting self-interacting dark matter in Crater II. Apu JL 968, L13; doi: 10.3847/2041-8213/ad50cd

Source: www.sci.news

Astrophysicist declares universe devoid of dark matter

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Professor Rajendra Gupta of the University of Ottawa is challenging current theoretical models of the composition of the universe by showing that there is actually no room for dark matter in the universe.

This artist's impression shows the evolution of the universe, starting with the Big Bang on the left and continuing with the emergence of the Cosmic Microwave Background. The formation of the first stars ends the Dark Ages of the universe, followed by the formation of galaxies. Image credit: M. Weiss / Harvard-Smithsonian Center for Astrophysics.

In cosmology, the term dark matter refers to anything that does not appear to interact with light or electromagnetic fields, or that can only be explained by gravity.

Although we can't see it and don't know what it's made of, it helps us understand how galaxies, planets, and stars work.

Professor Gupta reached this conclusion using a combination of covariation coupling constant (CCC) and “tired light” (TL) theory (CCC+TL model).

His model combines two ideas: how the forces of nature diminish over cosmic time and that light loses energy as it travels long distances.

It has been tested and shown to be consistent with several observations, including how galaxies spread and how light from the early universe evolved.

The discovery challenges the common understanding of the universe, which suggests that about 27% of the universe is made up of dark matter, less than 5% is normal matter, and the rest is dark energy.

“This new discovery confirms previous research, which found that the universe is 26.7 billion years old, and found that the existence of dark matter is not necessary for the universe,” said Gupta. the professor said.

“Standard cosmology says that the accelerating expansion of the universe is caused by dark energy, but it's actually because the forces of nature weaken as the universe expands, not by dark energy.”

In his research, Professor Gupta analyzed data from a recent paper on the distribution of galaxies at low redshifts and the angular size of the sound horizon in the literature at high redshifts.

“There are several papers that question the existence of dark matter, but to my knowledge, my paper does not support the existence of dark matter, while being consistent with the major cosmological observations that we have had time to confirm.” “This is the first paper to exclude ,” he said.

“By challenging the need for dark matter in the universe and providing evidence for a new cosmological model, this study opens up new avenues for exploring the fundamental properties of the universe.”

of paper Published in astrophysical journal.

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Rajendra P.Gupta other. 2024. Testing the CCC+TL cosmology with observed baryon acoustic vibration signatures. APJ 964, 55; doi: 10.3847/1538-4357/ad1bc6

Source: www.sci.news

Astrophysicist from Princeton solves the enigma of black hole jets and galactic ‘lightsabers’

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Princeton researchers have found that the M87* black hole emits energy outward, contributing to the formation of a giant jet. This discovery challenges traditional views about black holes and may be further tested with advanced telescopes. This new understanding opens up new avenues in comprehending black hole dynamics, though the source of the jet’s power is not definitively explained. This research was conducted with the support of the Princeton Gravity Initiative, a Taplin Fellowship, the National Science Foundation (grant 2307888), and a Simons Foundation Investigator Award.

The findings were published in the Astrophysical Journal on November 14, 2023. The research was spearheaded by Princeton astrophysicists including Andrew Chael, Alexandru Lupsasca, George N. Wong, and Eliot Quataert. With origins in Einstein’s theory of relativity, the researchers made intricate observations involving the black hole and its magnetic field to decipher the direction of energy flow. The researchers found that energy near the event horizon of black hole M87* is pushing outward rather than inward. They also verified the prediction that black holes lose rotational energy.

The researchers have concluded that while it is very likely that the black hole is powering the jet, it cannot be proven conclusively. Furthermore, the team has not conclusively shown that the black hole’s rotation “really powers the extragalactic jet.” Though the energy levels shown in their model were consistent with what a jet would require, they could not rule out the possibility that the jet could be powered by spinning plasma outside the black hole. Nevertheless, it is expected that the next generationEvent Horizon Telescope will further explore and confirm these findings.

The research team was also awarded the 2024 New Horizons Prize in Physics from the Breakthrough Prize Foundation for their black hole research. The research was also supported by a Taplin Fellowship, the National Science Foundation, a Simons Foundation Investigator Award as well as by the Princeton Gravity Initiative.

Source: scitechdaily.com