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Universe consisting of fuzzy dark matter galaxies visualized by researchers

Astronomers keen to understand the reasons for death of galaxies in the universe

Galaxies are getting killed in the extreme regions of the universe as their star formation is being closed and researchers are intrigued to know the reasons behind it. A new program termed as the Virgo Environment Traced in Carbon Monoxide survey (VERTICO) is investigating how the galaxies are being killed. 

Toby Brown, the principal investigator of VERTICO led a team of 30 experts using the Atacama Large Millimeter Array (ALMA) for mapping the molecular hydrogen gas, the fuel from which new stars are created, at a very high resolution in 51 galaxies in the Virgo Cluster, the nearest galaxy cluster. 

ALMA was commissioned in 2013 at a price of USD 1.4 billion. It is an array of connected radio dishes at a height of 5000 metres in Atacama Desert, Northern Chile. This is an international cooperation between the United States, Canada, Japan, Taiwan, Chile, South Korea and Europe. This is the largest astronomical project that is ground based and is the most advanced millimetre wavelength telescope to have been constructed. This is best suited to study cold gas clouds from which new stars are created that cannot be observed by visible light. Programs such as VERTICO are designed to address the issues leading to a major breakthrough in this domain. 

The location of galaxies in the universe and their interaction with surroundings are major influences in their ability to form stars. But it is unknown how this environment rules on the life and death of the galaxies. 

The galaxy clusters are the most massive environments in universe which contain many hundreds of galaxies. The presence of high gravitational forces results in high acceleration of the galaxies, superheating the plasma to extreme temperatures. In these dense interiors, galaxies interact with their surroundings that can kill their star formation. The main focus of VERTICO is to understand the mechanisms that remove star formation. 

When galaxies fall through clusters, the intergalactic plasma can remove the gas in a very violent process known as ram pressure stripping. Clearing the fuel for star formation can result in killing the galaxy where no new stars are formed. The high temperature in clusters can stop the cooling and condensing of hot gas onto galaxies. Here the gas is slowly consumed as stars are formed leading to a gradual shut down in formation of stars known as strangulation. 

These processes vary a lot but each leaves behind a unique imprint on the star forming gas of the galaxy. VERTICO aims to bring together a complete picture from each of these processes building on the previous work to understand the impact of environment on evolution of galaxy. 

As Virgo Cluster is the nearest massive cluster, we can capture snapshots of the different stages of the galaxies. As a result, a complete picture of how star formation is shut in the cluster galaxies can be built. Virgo Cluster galaxies have been observed at nearly all wavelengths of the spectrum the observations of the star forming gas along with the required sensitivity do not exist as of now. 

VERTICO aims to generate high resolution maps of the molecular hydrogen gas and understand the exact quenching mechanisms, ram pressure stripping responsible for killing the galaxies. This will improve the understanding of the evolution of galaxies in the densest places of the universe. 

 

artist impression naro

Cool, Nebulous Ring around Milky Way’s Supermassive Black Hole

Through decades of study, astronomers have developed a clearer picture of the chaotic and crowded neighborhood surrounding the supermassive black hole at the center of the Milky Way. Our galactic center is approximately 26,000 light-years from Earth and the supermassive black hole there, known as Sagittarius A* (A “star”), is 4 million times the mass of our Sun.

We now know that this region is brimming with roving stars, interstellar dust clouds, and a large reservoir of both phenomenally hot and comparatively colder gases. These gases are expected to orbit the black hole in a vast accretion disk that extends a few tenths of a light-year from the black hole’s event horizon.

Until now, however, astronomers have been able to image only the tenuous, hot portion of this flow of accreting gas, which forms a roughly spherical flow and showed no obvious rotation. Its temperature is estimated to be a blistering 10 million degrees Celsius (18 million degrees Fahrenheit), or about two-thirds the temperature found at the core of our Sun. At this temperature, the gas glows fiercely in X-ray light, allowing it to be studied by space-based X-ray telescopes, down to the scale of about a tenth of a light-year from the black hole.

In addition to this hot, glowing gas, previous observations with millimetre-wavelength telescopes have detected a vast store of comparatively cooler hydrogen gas (about 10 thousand degrees Celsius, or 18,000 degrees Fahrenheit) within a few light-years of the black hole. The contribution of this cooler gas to the accretion flow onto the black hole was previously unknown.

Although our galactic centre black hole is relatively quiet, the radiation around it is strong enough to cause hydrogen atoms to continually lose and recombine with their electrons. This recombination produces a distinctive millimetre-wavelength signal, which is capable of reaching Earth with very little losses along the way.

NRAO image the nebulous

ALMA image of the disk of cool hydrogen gas flowing around the supermassive black hole at the centre of our galaxy. The colors represent the motion of the gas relative to Earth: the red portion is moving away, so the radio waves detected by ALMA are slightly stretched, or shifted, to the “redder” portion of the spectrum; the blue colour represents gas moving toward Earth, so the radio waves are slightly scrunched, or shifted, to the “bluer” portion of the spectrum. Crosshairs indicate the location of the black hole.
Credit: ALMA (ESO/NAOJ/NRAO), E.M. Murchikova; NRAO/AUI/NSF, S. Dagnello

With its remarkable sensitivity and powerful ability to see fine details, the Atacama Large Millimeter/submillimeter Array (ALMA) was able to detect this faint radio signal and produce the first-ever image of the cooler gas disk at only about a hundredth of a light-year away (or about 1000 times the distance from the Earth to the Sun) from the supermassive black hole. These observations enabled the astronomers both to map the location and trace the motion of this gas. The researchers estimate that the amount of hydrogen in this cool disk is about one-tenth the mass of Jupiter, or one ten-thousandth of the mass of the Sun.

By mapping the shifts in wavelengths of this radio light due to the Doppler effect (light from objects moving toward the Earth is slightly shifted to the “bluer” portion of the spectrum while light from objects moving away is slightly shifted to the “redder” portion), the astronomers could clearly see that the gas is rotating around the black hole. This information will provide new insights into the ways that black holes devour matter and the complex interplay between a black hole and its galactic neighbourhood.

“We were the first to image this elusive disk and study its rotation,” said Elena Murchikova, a member in astrophysics at the Institute for Advanced Study in Princeton, New Jersey, and lead author on the paper. “We are also probing accretion onto the black hole. This is important because this is our closest supermassive black hole. Even so, we still have no good understanding of how its accretion works. We hope these new ALMA observations will help the black hole give up some of its secrets.”

Materials provided by NRAO