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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. 


Astronomers detect three supermassive black holes at the center of three colliding galaxies

Astronomers detect three supermassive black holes at the center of three colliding galaxies

Three supermassive black holes (SMBHs) glowing in x-ray emissions have been identified by astronomers at the center of three colliding galaxies a billion light-years away from Earth. All three black holes are active galactic nuclei(AGN), consuming material. This finding may clarify a long-standing issue in astrophysics and black hole mergers known as “final parsec problem”. The study appears in The Astrophysical Journal.

Researchers detected the three SMBHs with the data from several telescopes, Sloan Digital Sky Survey (SDSS,) the Chandra X-ray Observatory, and the Wide-field Infrared Survey Explorer (WISE)A nearly unbelievably astronomical event, the fusion of three galaxies may play a crucial role in how the most massive black holes expand over time.

Ryan Pfeifle from George Mason University in Fairfax, Virginia, the paper’s first author said that they found this incredible system through their selection technique while they were only looking for black hole pairs. He also added that this is the most powerful evidence found for such a triple system of active supermassive black holes. It is very challenging to locate triple black hole systems since they are wrapped in gas and dust. It took several telescopes functioning in different parts of the electromagnetic spectrum and also the work with researchers to detect these black holes.

Co-author Shobita Satyapal, also belonging to George Mason said that dual and triple black holes are extremely rare but such systems are actually a natural outcome of galaxy mergers, through which galaxies grow. This triple-merger was first spotted in visible light by the SDSS and only through a citizen science project named Galaxy Zoo the system of colliding galaxies was detected. The system was in a state of galaxy merger glowing in the infrared as seen by the WISE when more than one black holes were expected to be feeding.

Researchers shifted to the Chandra Observatory and the Large Binocular Telescope (LBT) for confirmation as Sloan and WISE data were fascinating clues. Chandra observations revealed bright x-ray sources in the galactic centers where SMBHs are expected to detect. Chandra and Nuclear Spectroscopic Telescope Array (NuSTAR) satellite of NASA discovered more shreds of evidence showing the presence of SMBHs and the existence of large amounts of gas and dust near one of them. It was expected in merging of black holes. Spectral evidence received by optical light data from SDSS and  LBT shows that these are characteristics of the feeding SMBHs.

Christina Manzano-King, co-author from the University of California, Riverside said that optical spectra include plenty of information about a galaxy which is frequently used to detect active accreting supermassive black holes and can tell about their influence on the inhabitant galaxies. Pfeifle said that they have found a new method of identifying triple supermassive black holes using these major observatories as each telescope gives them a distinct idea about these systems. They expect to extend their work to find more triples using the same method.

The final parsec problem is a theoretical problem that is fundamental to our understanding of binary black hole mergers that states that the enormous orbital energy of two approaching black holes stops them from merging. They can get separated by a few light-years, then the merging process stables.

The hyperbolic trajectories of two initially approaching black hole carry them right past each other. The two holes catapult the stars as they interact with them in their proximity transferring a fraction of their orbital energy to a star every time. The energy of the black holes gets reduced by the emission of gravitational waves. The two black holes finally slow down and approach each other more closely shedding enough orbital energy finally getting within just a few parsecs of each other. More matter is discharged via sling-shotting as they come closer. As a result, for the black holes, no more matter is left to interact with and shed more orbital energy. The merging process halts.

Astronomers know that strong gravitational waves are responsible for black hole mergers.LIGO (Laser Interferometry Gravitational-Wave Observatory) discovers a black hole merger almost every week. The final parsec problem is about how they merge with each other finally. Researchers think that a third black hole like seen in this system could give the push needed for the black holes to get merged. Nearly 16% of supermassive black hole pairs in colliding galaxies are expected to interact with a third supermassive black hole before they merge.

The challenge is that gravitational waves produced during merging would be too low-frequency for LIGO or the VIRGO observatory to detect. Researchers may have to depend on future observatories like LISA, ESA/NASA’s Laser Interferometer Space Antenna to detect those waves. LISA is better-equipped than LIGO or VIRGO to detect merging of giant and massive black holes as it can detect lower frequency gravitational waves.

Reference: The Astrophysical Journal.

Massive Galaxy Formation

Researchers create Universe Machine to understand the formation and evolution of galaxies

The science behind the formation of galaxies and their evolution has remained a puzzle for decades, but the answer might be found soon with the help of simulations carried using supercomputers by a group of scientists from the University of Arizona.

Observation of galaxies can only provide their snapshots over time however understanding their evolution requires computer simulations. Astronomers have used this technique for testing different theories of the formation of galaxies. Peter Behroozi, an assistant professor at the UA Steward Observatory generated millions of universes on a supercomputer, each having different physical theories on the formation of galaxies. The paper has been published in Monthly Notices of the Royal Astronomical Society. It challenges the conventional ideas on the role of dark matter in galaxy formation and the evolution of galaxies.

Universes are created on the supercomputer and then compared to real ones which help in identifying the rules. This research managed to create self-consistent universes for the first time which are replicas of the real one and simulations which contain 12 million galaxies spanning over 400 million years.

The universes were put through several tests to understand how galaxies appeared in the simulated universe compared to the real one. The universe resembling ours had similar physical rules.

The results from “UniverseMachine” have helped to resolve as to why galaxies stop making new stars even when plenty of hydrogen gas and other raw materials are present.

The classical theories suggest the presence of supermassive black holes in the galactic centres prevent gases to cool down to form stars. Similarly, dark matter heats up the surrounding gas and prevents forming stars. However, it was found that many galaxies in the universe were more likely to form stars at higher rates which is a contradiction. The team then created virtual galaxies in which the opposite happened. The universe based on current theories which stopped star formation early on appear much redder they actually are. The galaxy appears red due to its age and moving away faster, which shifts the light into the red spectrum called “redshift”. Also if a galaxy stops forming stars, there will be lesser blue stars and old red stars will be left.

If galaxies stopped creating stars, the colour of the universe would have been entirely different, hence it can be concluded that galaxies formed stars more efficiently in the earlier than we expected and the energy from the black holes and exploding stars is less efficient in decreasing the formation of stars.

A mock universe requires huge complexity which requires an entirely new approach not limited by computing power or memory and provided enough resolution to observe both supernovae as well as a major portion of the universe. Simulating a galaxy needs 10 to the 48th computing operations. The team used the “Ocelote” supercomputer at the UA High-Performance Computing cluster. 2000 processors churned the data for three weeks and over the course of the project, the team generated 8 million universes. The team took past 20 years of observations and compared them to the millions of mock universes generated and checked for matches. They plan to expand the UniverseMachine to include the morphology of galaxies and how their shapes evolve over time.

Journal Reference: Monthly Notices of the Royal Astronomical Society

A 3-D model of the Milky Way Galaxy using data from Cepheids

Astronomers generate the largest 3D model of Milky Way using Cepheid data

We do not possess a GPS system for our twisted and warped galaxy. As a result, astronomers have to be crafty for pointing our location among stars and producing maps of the Milky Way galaxy. Astronomers from the US and Europe successfully managed to create a 3D model of Milky Way galaxy which is based on the interstellar distance. The study has been published in the Science journal

It draws on the population of stars that are called Cepheids. They are massive, young, pulsing stars having brightness more than that of the Sun. The University of Warsaw ran a sky survey with the help of data from the Optical Gravitational Lensing Experiment from Las Campanas Observatory in Chile. Researchers managed to pick out 2,431 Cepheids through the thick dust and gas of Milky Way and used them for generating the map of the galaxy. 

Dorota Skowron, a researcher with Wroclaw University of Science and Technology and the study’s lead author said that the OGLE project observed the Milky Way’s galactic disk for a period of six years while capturing 206,726 sky images that contained 1,055,030,021 stars. In this they found the Cepheids population to be very useful for the purpose of map plotting since their brightness varies over time. 

This allowed the researchers to observe how bright the star actually is versus how it appears from the Earth. This difference between the two can inform us how far the star is from our Sun. With the help of this fluctuation, scientists produced the galaxy’s 3D model which confirmed the previous work that the galaxy is flared at the edges. They were able to determine the Cepheid’s age where the younger stars were closer to the center and older stars farther away from the galactic disk. 

With the simulation of star formation in the early Milky Way, scientists showed the evolution of the galaxy in past 175 million years with star formation in spiral arms resulting in distribution of Cepheids from 20 million to 260 million years old. Skowron hopes that the paper will be a good initial point for sophisticated modeling of our Galaxy’s past, as the Cepheids are a great testbed for checking the accuracy of the models. 

A study was earlier published in Nature Astronomy which looked at 1339 Cepheids and generated a comprehensive 3D map of Milky Way which found that our galaxy is twisted at the edges. It observed stars from the Wide-field Infrared Survey Explorer (WISE) of NASA. These two studies produced similar results which found about the warped edges of Milky Way. Both the studies relied on the fact that the Cepheids are present on our side of the Milky Way. An important question is whether there is a similar warp in the opposite side too.

Skowron does not think observing the other side will increase the probability of finding Cepheids. The future projects will observe the pulsing star found in our Galaxy called  RR Lyrae. They are present from an earlier time in the Milky Way and can provide another way of mapping the Galaxy. 

Journal Reference: Science journal

black hole eating star

Researchers solve the mystery of small galaxies with supermassive black holes

Nearly every galaxy in the universe appears to have a black hole in the centre including our Milky Way galaxy. There is a strange relationship between the mass of black hole at the galactic centre and properties of the galactic host itself. So a bigger galaxy refers to a bigger black hole. However, some exceptions have been found to this trend and researchers have detected an important link between the evolution of galaxies and black holes.

We do not know which came first, the black hole or the galaxy. About thirteen and a half billion years ago galaxies and black holes formed nearly at the same time. According to astronomers, regular communication takes place between galaxies and their black holes. Bigger galaxies have more matter to feed their giant black holes. On feeding, the black holes become active. Gases swirl around it with high energies before falling onto the event horizon. Some part of the gas heats and radiation is emitted which escapes the vicinity. Gases can also swirl around the outer edges without falling in which form of long jets extending thousands of light-years in the nearby medium.

So, this energy which is dumped in the surrounding heats up the nearby gases and the heated gas has low inclination to sink into the centre where it might encounter the black hole. Thus the gas stays away and the black hole stabilizes in size as it cannot feed on anything. If a galaxy grows larger, then it can press more gas to the centre feeding the black hole followed by a feedback episode which holds the continued growth of black hole from getting out of control.

Thus smaller galaxies end up with smaller black holes and the larger ones with big black holes. However, there are exceptions to it, as some galaxies host the black holes way out of their ability to feed them. The reason could be due to a peculiar type of galaxy known as a blue nugget. These galaxies are found very far away meaning they were part of a younger universe. They are blue and small as their name suggests. They have an enhanced rate of star formation. Due to this, they form bigger and brighter stars than average. They are able to form stars at an exceptional rate since they feed on the nearby gas streams pumping material to the undersized galaxy.

However, this influx of raw material has its impacts and due to these activities, a massive black hole formation takes place at the centre. It feeds all over the galaxy shutting the further formation of stars. Due to their size, this event affects the entire galaxy terminating the growth at an early stage. So the stars which were formed eventually die as old, dim, red stars turning the galaxy into a red nugget. Thus it has an exceptionally large black hole at the centre. There are only handful of examples of such cases which can give insights into the relationship between galaxies and their black holes.

Journal Reference: arxiv

AGN Inner Structure

Radiation from black holes may create life

Black holes are seen as an engine of destruction on a cosmic scale but soon are also recently seen as the bringers of life. Recently, it was discovered that the black holes emit radiation during feeding frenzies and create molecular building blocks and can even power photosynthesis.

A new study published in Astrophysical Journal used computer models to look at the radiating disks of gas and dust called the active galactic nuclei (AGN) which swirl around the massive black holes. The AGN is formed when the black hole’s gravity binds matter together. A lot of light and radiation is created as the matter swirls around a black hole.

Earlier it was suspected that radiation would create a dead zone around the AGN and could explain why we haven’t seen any complex extraterrestrial life towards the Milky Way. Sagittarius A is 3200 light years away and is the black hole of our galaxy. People mostly talk about the detrimental effects of the black hole but astronomers at Harvard University wanted to reexamine the black hole to find out the positive effects of the black hole.

There stands a chance for hosting life in regions with the atmosphere thicker than those of Earth and those who are far away from the AGN to retain the atmosphere. There is a special zone called Goldilocks Zone which gets just the right amount of ultraviolet radiation. These radiations could break apart compounds, molecules creating necessary building blocks such as protein, lipids, and DNA.

The Goldilocks zone is around 140 light years away from the center of the black hole and 1 light year is equivalent to 5.8 million million miles. AGN emits a lot of light which can be used up by plants for photosynthesis. This light would be particularly important for free-floating planets that do not have a host star.

A large area in several galaxies might have AGN powered photosynthesis especially those galaxies which have supermassive black holes like our galaxy. For a galaxy similar to our own, the region would extend to 1100 light years from the galaxy centre. The negative effects due to ultraviolet and X-Ray, the adverse consequences were exaggerated and that bacteria on Earth have created bio films to protect itself from ultraviolet rays and areas with heavy UV radiation would have developed similar techniques for ultraviolet protection. X rays and gamma rays are readily absorbed by Earth like atmospheres and that the damaging effects of AGN would end around 100 light years from Sagittarius A.

Accretion disk

Researchers announce discovery that can change the concept of death of galaxies

At American Astronomical Society‘s annual meeting in St. Louis, Missouri, Allison Kirkpatrick, assistant professor in physics and astronomy at the University of Kansas, will present the discovery of “cold quasars“. These are the galaxies with a huge amount of cold gas but can still produce new stars in spite of a quasar located at the centre. This breakthrough finding turns down many assumptions regarding the maturation of galaxies and it represents a phase in the life cycle of the galaxy which was not yet known.

A quasar which stands for quasi-stellar radio source can be described as a supermassive black hole on steroids. When gas falls toward a quasar at the galaxy’s centre it forms an accretion disk which has the potential to generate a huge amount of electromagnetic energy that has luminosity, hundred times more than a normal galaxy. It has been thought till now, that when a quasar forms, it signals the end of the galaxy’s ability to form new stars.

Kirkpatrick remarked that the gas which is accreting on the black hole gets heated and it forms X-rays. The light wavelength is a direct correspondence of the amount of heat. When something generates X-rays, then it is one of the hottest things in the universe. Humans, on the other hand, produce infrared light. After the accretion of the gas on the black hole, it moves at relativistic speeds and thus forms a magnetic field around gas. Similar to solar flares, there can be materials shooting off from the black hole. This essentially cuts off the gas supply in the galaxy, as a result, it loses the ability to form stars.

However, in the survey conducted by Kirkpatrick, nearly 10 percent of the galaxies with accreting black holes had a supply of cold gas remaining even after this phase and formed new stars. This is highly surprising and these are very unique objects. Out of this, a further 10 percent is even more unexpected. These are blue sources which resemble the end stages of a supermassive black hole. They are evolving to passive elliptical galaxy yet have a huge amount of cold gas in them. These are called cold quasars.

Kirkpatrick said that these galaxies are very rare and they have been observed in the transition period right before the star formation in the galaxy is over. These objects were first identified in the Sloan Digital Sky  – the detailed map of the universe. They were surveyed with the help of XMM Newton Telescope and Herschel Space Telescope. Next up, Kirkpatrick wants to determine if this occurs to every galaxy or a specific group of galaxies.

Galactic maturity

Image: Mature Galaxy Mesmerizes in New Hubble View

This striking image was taken by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3), a powerful instrument installed on the telescope in 2009. WFC3 is responsible for many of Hubble’s most breathtaking and iconic photographs.

Shown here, NGC 7773 is a beautiful example of a barred spiral galaxy. A luminous bar-shaped structure cuts prominently through the galaxy’s bright core, extending to the inner boundary of NGC 7773’s sweeping, pinwheel-like spiral arms. Astronomers think that these bar structures emerge later in the lifetime of a galaxy, as star-forming material makes its way towards the galactic center — younger spirals do not feature barred structures as often as older spirals do, suggesting that bars are a sign of galactic maturity. They are also thought to act as stellar nurseries, as they gleam brightly with copious numbers of youthful stars.

Our galaxy, the Milky Way, is thought to be a barred spiral like NGC 7773. By studying galactic specimens such as NGC 7773 throughout the universe, researchers hope to learn more about the processes that have shaped — and continue to shape — our cosmic home.

NGC 1052 DF2 ghostly galaxy lacking dark matter

Researchers solve the mystery of galaxy which is void of dark matter

An earlier discovery that a galaxy without dark matter existed was indeed a mystery and was incompatible according to current theories however it has now been resolved. According to a new analysis the NGC1052-DF2 galaxy which was found last year is closer to us than expected and previously calculated, which means it is likely to contain dark matter. The study has been published in the Monthly Notices of the Royal Astronomical Society.

Dark matter is indeed a big mystery in itself as we cannot detect that it exists and even we do not know it exists but we know it is present which creates the effect of mass in the universe. Objects in the galaxies move faster than they should be moving because of this undetectable force due to the extra mass of dark matter which in turn generates more gravitational force than normal.

Dark matter is fundamental to our understanding of the universe. It has helped in the formation of stars and galaxies from the primaeval soup that existed after big bang and dark matter is what prevents bodies in the galaxy from just flying off into the unknown.

After reading and seeing the formation of the NGC1052-DF2 galaxy it changes the way as to how we think galaxies are formed. For decades we have thought that galaxies were formed due to dark matter and later forms stars due to the gases present in the dark matter. It is a critical ingredient in understanding the universe.

An international team of researchers led by the Instituto de Astrofísica de Canarias (IAC) decided to take a closer look at this galaxy and found out that anomalous measurements that were recorded in previous research have pointed out the absence of dark matter was dependant on the distance to the galaxy around 64 million light years away. Researchers used five separate telescopes including Hubble and the Gemini Observatory to recalculate the distance to NGC1052-DF2 galaxy.

The distance obtained was close to 42 million light years away instead of 62 million light years which was recorded earlier and based on this, the mass of galaxy was half as less than it was previously assumed to be and the stars were about a quarter their weight. This galaxy has lesser mass but the existing mass contains more dark matter than traditional matter. The previous theory of absence of dark matter was due to the slow movement of star clusters however now the movement seems normal. It now appears as an ordinary low brightness galaxy with plenty of room for dark matter. More such galaxies exist where absence of dark matter is speculated, the NGC1052-DF4 being a similar case.

Dark Matter Cloud

Scientists confirm presence of Dark Matter, removing the existing doubts

The universe as we all know is a big and vast collection of planets, stars and galaxies which is spread across a diameter of 10 billion light years. However, the universe at the same time is a huge area full of mystery and dilemma which is constantly being observed and studied by our scientists in search of a clue to solve the puzzle of this great universe which we all a small part of. A curious mind often wonders what this entire universe is made of. This question has been bothering astrophysicists for a long time until lately a term called Dark Matter was termed.

Dark Matter is thought to account for 90-95% of the mass of the universe. The rest 5% mass is believed to be from the stars, galaxies and planets that are in the universe. It is believed to consist of non-luminous material that is thought about as existing in space. It is unlike normal matter as it cannot interact with electromagnetic force and cannot absorb light nor is able to reflect light that falls on it, thus making it harder to spot. Matter when exits exert a gravitational effect around it. Recently though, the existence of dark matter has been brought into question.

Chiara Di Paolo, a doctoral student of astrophysics at SISSA, has said that three years ago, a few colleagues of the Case Western Reserve University strongly questioned the understanding of the universe and therefore the in-depth work of the many researchers, casting doubt on the existence of matter within the galaxies. The reports have been published in The Astrophysical Journal.

After analysis of the rotation curves of 153 curves, an empirical relationship between the total gravitational acceleration of stars was obtained, observed and the component which would be observed in absence of dark matter and presence of ordinary matter as considered in the classical Newtonian theory.

Later Paolo Salucci, a professor of astrophysics at SISSA has stated that they had studied the relationship between total acceleration and its ordinary component in 106 galaxies, obtaining different results from those that had been previously observed from the case of ordinary matter. Thus the variation in results obtained by considering the presence of ordinary matter and the results obtained practically in space which is dark matter is different. He further stated in his statement that the recent developments not only demonstrates the inexactness of the empirical relationship previously described but removes doubts on the existence of dark matter in the galaxies.

Topics such as these continuously being explored and questioned by curious minds all across the world. These theories are constantly questioned in pursuit to prove it, we keep discovering newer things in the ever-changing and mysterious world of physics and astrophysics.