Saturday, April 15, 2023

SPACE NEWS

Giant Galaxy Seen in 3D by NASA's Hubble Space Telescope and Keck Observatory


Peer-Reviewed Publication

NASA/GODDARD SPACE FLIGHT CENTER

HUBBLE IMAGE AND 3D MODEL OF M87 

IMAGE: A PHOTO OF THE HUGE ELLIPTICAL GALAXY M87 [LEFT] IS COMPARED TO ITS THREE-DIMENSIONAL SHAPE AS GLEANED FROM METICULOUS OBSERVATIONS MADE WITH THE HUBBLE AND KECK TELESCOPES [RIGHT]. BECAUSE THE GALAXY IS TOO FAR AWAY FOR ASTRONOMERS TO EMPLOY STEREOSCOPIC VISION, THEY INSTEAD FOLLOWED THE MOTION OF STARS AROUND THE CENTER OF M87, LIKE BEES AROUND A HIVE. THIS CREATED A THREE-DIMENSIONAL VIEW OF HOW STARS ARE DISTRIBUTED WITHIN THE GALAXY. view more 

CREDIT: ILLUSTRATION: NASA, ESA, JOSEPH OLMSTED (STSCI), FRANK SUMMERS (STSCI) SCIENCE: CHUNG-PEI MA (UC BERKELEY)

Though we live in a vast three-dimensional universe, celestial objects seen through a telescope look flat because everything is so far away. Now for the first time, astronomers have measured the three-dimensional shape of one of the biggest and closest elliptical galaxies to us, M87. This galaxy turns out to be "triaxial," or potato-shaped. This stereo vision was made possible by combining the power of NASA's Hubble Space Telescope and the ground-based W. M. Keck Observatory on Maunakea, Hawaii.

In most cases, astronomers must use their intuition to figure out the true shapes of deep-space objects. For example, the whole class of huge galaxies called "ellipticals" look like blobs in pictures. Determining the true shape of giant elliptical galaxies will help astronomers understand better how large galaxies and their central large black holes form.

Scientists made the 3D plot by measuring the motions of stars that swarm around the galaxy's supermassive central black hole. The stellar motion was used to provide new insights into the shape of the galaxy and its rotation, and it also yielded a new measurement of the black hole's mass. Tracking the stellar speeds and position allowed researchers to build a three-dimensional view of the galaxy.

Astronomers at the University of California, Berkeley, were able to determine the mass of the black hole at the galaxy's core to a high precision, estimating it at 5.4 billion times the mass of the Sun. Hubble observations in 1995 first measured the M87 black hole as being 2.4 billion solar masses, which astronomers deduced by clocking the speed of the gas swirling around the black hole. When the Event Horizon Telescope, an international collaboration of ground-based telescopes, released the first-ever image of the same black hole in 2019, the size of its pitch-black event horizon allowed researchers to calculate a mass of 6.5 billion solar masses using Einstein's theory of general relativity.

The stereo model of M87 and the more precise mass of the central black hole could help astrophysicists learn the black hole's spin rate. "Now that we know the direction of the net rotation of stars in M87 and have an updated mass of the black hole, we can combine this information with data from the Event Horizon Telescope to constrain the spin," said Chung-Pei Ma, a UC Berkeley lead investigator on the research.

Over ten times the mass of the Milky Way, M87 probably grew from the merger of many other galaxies. That's likely the reason M87's central black hole is so large – it assimilated the central black holes of one or more galaxies it swallowed.

Ma, together with UC Berkeley graduate student Emily Liepold (lead author on the paper published in the Astrophysical Journal Letters) and Jonelle Walsh at Texas A&M University were able to determine the 3D shape of M87 thanks to a new precision instrument mounted on the Keck II Telescope. They pointed Keck at 62 adjacent locations of the galaxy, mapping out the spectra of stars over a region about 70,000 light-years across. This region spans the central 3,000 light-years where gravity is largely dominated by the supermassive black hole. Though the telescope cannot resolve individual stars because of M87's great distance, the spectra can reveal the range of velocities to calculate mass of the object they're orbiting.

"It's sort of like looking at a swarm of 100 billion bees," said Ma. "Though we are looking at them from a distance and can't discern individual bees, we are getting very detailed information about their collective velocities."

The researchers took the data between 2020 and 2022, as well as earlier star brightness measurements of M87 from Hubble, and compared them to computer model predictions of how stars move around the center of the triaxial-shaped galaxy. The best fit to this data allowed them to calculate the black hole's mass. "Knowing the 3D shape of the 'swarming bees' enabled us to obtain a more robust dynamical measurement of the mass of the central black hole that is governing the bees' orbiting velocities," said Ma.

In the 1920s, astronomer Edwin Hubble first classified galaxies according to their shapes. Flat disk spiral galaxies could be viewed from various projection angles of the sky: face-on, oblique, or edge-on. But the "blobby-looking" galaxies were more problematic to characterize. Hubble came up with the term elliptical. They could only be sorted out by how great the ellipticity was. They didn't have any apparent dust or gas inside of them for better distinguishing between them. Now, a century later astronomers have a stereoscopic look at a prototypical elliptical galaxy.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble and Webb science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

3D MODEL OF M87 [VIDEO] 

How different were galaxies in the early universe?

Astronomers are one step closer to discovering the secrets of the cosmic dawn

Peer-Reviewed Publication

MCGILL UNIVERSITY

The HERA radio telescope at night 

IMAGE: THE HERA RADIO TELESCOPE, LOCATED IN KAROO IN SOUTH AFRICA, CONSISTS OF 350 DISHES POINTED UPWARD TO DETECT RADIO WAVES FROM THE EARLY UNIVERSE. view more 

CREDIT: DARA STORER

An array of 350 radio telescopes in the Karoo desert of South Africa is getting closer to detecting the “cosmic dawn” — the era after the Big Bang when stars first ignited and galaxies began to bloom.

A team of scientists from across North America, Europe, and South Africa has doubled the sensitivity of a radio telescope called the Hydrogen Epoch of Reionization Array (HERA). With this breakthrough, they hope to peer into the secrets of the early universe.

“Over the last couple of decades, teams from around the world have worked towards a first detection of radio waves from the cosmic dawn. While such a detection remains elusive, HERA’s results represent the most precise pursuit to date,” says Adrian Liu, an Assistant Professor at the Department of Physics and the Trottier Space Institute at McGill University.

The array was already the most sensitive radio telescope in the world dedicated to exploring the cosmic dawn. Now the HERA team has improved its sensitivity by a factor of 2.1 for radio waves emitted about 650 million years after the Big Bang and 2.6 for radio waves emitted about 450 million years after the Big Bang. Their work is described in a paper published in The Astrophysical Journal.

Although the scientists have yet to detect radio emissions from the end of the cosmic dark ages, their results provide clues about the composition of stars and galaxies in the early universe. So far, their data suggest that early galaxies contained very few elements besides hydrogen and helium, unlike our galaxies today. Today’s stars, have a variety of elements, ranging from lithium to uranium, that are heavier than helium.

Ruling out some theories

When the radio dishes are fully online and calibrated, the team hopes to construct a 3D map of the bubbles of ionized and neutral hydrogen – markers for early galaxies – as they evolved from about 200 million years to around 1 billion years after the Big Bang. The map could tell us how early stars and galaxies differed from those we see around us today, and how the universe looked in its adolescence, say the researchers.

According to the researchers, the fact that the HERA team has not yet detected these signals rules out some theories of how stars evolved in the early universe. “Our data suggest that early galaxies were about 100 times more luminous in X-rays than today’s galaxies. The lore was that this would be the case, but now we have actual data that bolsters this hypothesis,” says Liu.

Waiting for a signal

The HERA team continues to improve the telescope’s calibration and data analysis in hopes of seeing those bubbles in the early universe. However, filtering out the local radio noise to see the signals from the early universe has not been easy. “If it’s Swiss cheese, the galaxies make the holes, and we’re looking for the cheese,” says David DeBoer, a research astronomer in University of California Berkeley’s Radio Astronomy Laboratory.

“HERA is continuing to improve and set better and better limits,” says Aaron Parsons, principal investigator for HERA and a University of California Berkeley Associate Professor of astronomy. “The fact that we’re able to keep pushing through, and we have new techniques that are continuing to bear fruit for our telescope, is great.”

The HERA collaboration is led by University of California Berkeley and includes scientists from across North America, Europe, and South Africa, with support in Canada from Natural Sciences and Engineering Research Council of Canada, Canadian Institute for Advanced Research, Fonds de recherche du Québec – Nature et technologies, and from the Trottier Space Institute at McGill University. The construction of the array is funded by the National Science Foundation, the Alfred P. Sloan Foundation, and the Gordon and Betty Moore Foundation, with key support from the government of South Africa and the South African Radio Astronomy Observatory (SARAO).

About the study

Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray Heating of the IGM with HERA Phase I Observations” by the HERA Collaboration was published in The Astrophysical Journal.

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