Gillian Wilson

Scientists precisely measure total amount of matter in the universe

Anonymous — Mon, 28 Sep 2020 14:39:26 +0000

Scientists precisely measure total amount of matter in the universe Anonymous (not verified) Mon, 09/28/2020 - 07:39 More News Iqbal Pittalwala | UCR News September 28, 2020

A top goal in cosmology is to precisely measure the total amount of matter in the universe, a daunting exercise for even the most mathematically proficient. A team led by scientists at the University of California, Riverside, has now done just that.

Reporting in the Astrophysical Journal, the team determined that matter makes up 31% of the total amount of matter and energy in the universe, with the remainder consisting of dark energy.

Mohamed Abdullah

“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 first author Mohamed Abdullah, a graduate student in the UCR Department of Physics and Astronomy. “However, since we know 80% 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.”

Abdullah explained that one well-proven technique for determining the total amount of matter in the universe is to compare the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations. Because present-day galaxy clusters have formed from matter that has collapsed over billions of years under its own gravity, the number of clusters observed at the present time is very sensitive to cosmological conditions and, in particular, the total amount of matter.

Gillian Wilson

“A higher percentage of matter would result in more clusters,” Abdullah said. “The ‘Goldilocks’ challenge for our team was to measure the number of clusters and then determine which answer was ‘just right.’ But it is difficult to measure the mass of any galaxy cluster accurately because most of the matter is dark so we can’t see it with telescopes.”

To overcome this difficulty, the UCR-led team of astronomers first developed “GalWeight”, a cosmological tool to measure the mass of a galaxy cluster using the orbits of its member galaxies. The researchers then applied their tool to observations from the Sloan Digital Sky Survey (SDSS) to create “GalWCat19,” a publicly available catalog of galaxy clusters. Finally, they compared the number of clusters in their new catalog with simulations to determine the total amount of matter in the universe.

“We have succeeded in making one of the most precise measurements ever made using the galaxy cluster technique,” said coauthor Gillian Wilson, a professor of physics and astronomy at UCR in whose lab Abdullah works. “Moreover, this is the first use of the galaxy orbit technique which has obtained a value in agreement with those obtained by teams who used noncluster techniques such as cosmic microwave background anisotropies, baryon acoustic oscillations, Type Ia supernovae, or gravitational lensing.”

The team determined that matter makes up about 31% of the total amount of matter and energy in the universe. Cosmologists believe about 20% of the total matter is made of regular — or “baryonic” matter — which includes stars, galaxies, atoms, and life, while about 80% is made of dark matter, whose mysterious nature is not yet known but may consist of some as-yet-undiscovered subatomic particle. (UCR/Mohamed Abdullah)

“A huge advantage of using our GalWeight galaxy orbit technique was that our team was able to determine a mass for each cluster individually rather than rely on more indirect, statistical methods,” said the third coauthor Anatoly Klypin, an expert in numerical simulations and cosmology.

By combining their measurement with those from the other teams that used different techniques, the UCR-led team was able to determine a best combined value, concluding that matter makes up 31.5±1.3% of the total amount of matter and energy in the universe.

The study was supported by grants from the National Science Foundation and NASA.

The research paper is titled “Cosmological Constraints on Ωm and σ8 from Cluster Abundances using the GalWCat19 Optical-spectroscopic SDSS Catalog.”

Like Goldilocks, the team compared the number of galaxy clusters they measured with predictions from numerical simulations to determine which answer was “just right.” (UCR/Mohamed Abdullah)

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Astronomers discover unusual monster galaxy in the very early universe

Anonymous — Tue, 11 Feb 2020 19:00:39 +0000

Astronomers discover unusual monster galaxy in the very early universe Anonymous (not verified) Tue, 02/11/2020 - 11:00 More News IQBAL PITTALWALA | UCR News February 05, 2020 https://news.ucr.edu/articles/2020/02/05/astronomers-discover-unusual-monster-galaxy-very-early-universe

An international team of astronomers led by scientists at the University of California, Riverside, has found an unusual monster galaxy that existed about 12 billion years ago, when the universe was only 1.8 billion years old.

Dubbed XMM-2599, the galaxy formed stars at a high rate and then died. Why it suddenly stopped forming stars is unclear.

“Even before the universe was 2 billion years old, XMM-2599 had already formed a mass of more than 300 billion suns, making it an ultramassive galaxy,” said Benjamin Forrest, a postdoctoral researcher in the UC Riverside Department of Physics and Astronomy and the study’s lead author. “More remarkably, we show that XMM-2599 formed most of its stars in a huge frenzy when the universe was less than 1 billion years old, and then became inactive by the time the universe was only 1.8 billion years old.”

The team used spectroscopic observations from the W. M. Keck Observatory’s powerful Multi-Object Spectrograph for Infrared Exploration, or MOSFIRE, to make detailed measurements of XMM-2599 and precisely quantify its distance.

Study results appear in the Astrophysical Journal.

The three panels show, from top to bottom, what XMM-2599’s evolutionary
trajectory might be, beginning as a dusty star-forming galaxy, then becoming
a dead galaxy, and perhaps ending up as a “brightest cluster galaxy,”or BCG.
(NRAO/AUI/NSF/B. Saxton; NASA/ESA/R. Foley; NASA/StScI)

“In this epoch, very few galaxies have stopped forming stars, and none are as massive as XMM-2599,” said Gillian Wilson, a professor of physics and astronomy at UCR in whose lab Forrest works. “The mere existence of ultramassive galaxies like XMM-2599 proves quite a challenge to numerical models. Even though such massive galaxies are incredibly rare at this epoch, the models do predict them. The predicted galaxies, however, are expected to be actively forming stars. What makes XMM-2599 so interesting, unusual, and surprising is that it is no longer forming stars, perhaps because it stopped getting fuel or its black hole began to turn on. Our results call for changes in how models turn off star formation in early galaxies.”

The research team found XMM-2599 formed more than 1,000 solar masses a year in stars at its peak of activity — an extremely high rate of star formation. In contrast, the Milky Way forms about one new star a year.

“XMM-2599 may be a descendant of a population of highly star-forming dusty galaxies in the very early universe that new infrared telescopes have recently discovered,” said Danilo Marchesini, an associate professor of astronomy at Tufts University and a co-author on the study.

The evolutionary pathway of XMM-2599 is unclear.

“We have caught XMM-2599 in its inactive phase,” Wilson said. “We do not know what it will turn into by the present day. We know it cannot lose mass. An interesting question is what happens around it. As time goes by, could it gravitationally attract nearby star-forming galaxies and become a bright city of galaxies?”

Co-author Michael Cooper, a professor of astronomy at UC Irvine, said this outcome is a strong possibility.

“Perhaps during the following 11.7 billion years of cosmic history, XMM-2599 will become the central member of one of the brightest and most massive clusters of galaxies in the local universe,” he said. “Alternatively, it could continue to exist in isolation. Or we could have a scenario that lies between these two outcomes.”

The team has been awarded more time at the Keck Observatory to follow up on unanswered questions prompted by XMM-2599.

“We identified XMM-2599 as an interesting candidate with imaging alone,” said co-author Marianna Annunziatella, a postdoctoral researcher at Tufts University. “We used Keck to better characterize and confirm its nature and help us understand how monster galaxies form and die. MOSFIRE is one of the most efficient and effective instruments in the world for conducting this type of research.”

Other researchers taking part include Daniel Lange-Vagle and Theodore Peña of Tufts University; Adam Muzzin and Cemile Marsan of York University, Canada; Ian McConachie and Jeffrey Chan of UCR; Percy Gomez of Keck Observatory; Erin Kado-Fong of Princeton University; Francesco La Barbera of INAF–Osservatorio Astronomico di Capodimonte, Italy; Ivo Labbe of Swinburne University of Technology, Australia; Julie Nantais of Andrés Bello National University, Santiago, Chile; Mario Nonino of Astronomical Observatory of Trieste, Italy; Paolo Saracco of Astronomical Observatory of Brera, Italy; Mauro Stefanon of Leiden University, Netherlands; and Remco F. J. van der Burg of the European Southern Observatory, Germany.

Wilson led the W. M. Keck Observatory data acquisition. Forrest led the processing and analysis.

The study was supported by grants from the National Science Foundation and NASA.

Header image shows Gillian Wilson (left) and Benjamin Forrest. (UCR/I. Pittalwala)