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Study Reveals Six Galaxies Undergoing Sudden, Dramatic Transitions

Galaxies come in a wide variety of shapes, sizes and brightnesses, ranging from humdrum ordinary galaxies to luminous active galaxies. While an ordinary galaxy is visible mainly because of the light from its stars, an active galaxy shines brightest at its center, or nucleus, where a supermassive black hole emits a steady blast of bright light as it voraciously consumes nearby gas and dust.

Sitting somewhere on the spectrum between ordinary and active galaxies is another class, known as low-ionization nuclear emission-line region (LINER) galaxies. While LINERs are relatively common, accounting for roughly one-third of all nearby galaxies, astronomers have fiercely debated the main source of light emission from LINERs. Some argue that weakly active galactic nuclei are responsible, while others maintain that star-forming regions outside the galactic nucleus produce the most light.

A team of astronomers observed six mild-mannered LINER galaxies suddenly and surprisingly transforming into ravenous quasars–home to the brightest of all active galactic nuclei. The team reported their observations, which could help demystify the nature of both LINERs and quasars while answering some burning questions about galactic evolution, in the Astrophysical Journal on September 18, 2019. Based on their analysis, the researchers suggest they have discovered an entirely new type of black hole activity at the centers of these six LINER galaxies.

“For one of the six objects, we first thought we had observed a tidal disruption event, which happens when a star passes too close to a supermassive black hole and gets shredded,” said Sara Frederick, a graduate student in the University of Maryland Department of Astronomy and the lead author of the research paper. “But we later found it was a previously dormant black hole undergoing a transition that astronomers call a ‘changing look,’ resulting in a bright quasar. Observing six of these transitions, all in relatively quiet LINER galaxies, suggests that we’ve identified a totally new class of active galactic nucleus.”

All six of the surprising transitions were observed during the first nine months of the Zwicky Transient Facility (ZTF), an automated sky survey project based at Caltech’s Palomar Observatory near San Diego, California, which began observations in March 2018. UMD is a partner in the ZTF effort, facilitated by the Joint Space-Science Institute (JSI), a partnership between UMD and NASA’s Goddard Space Flight Center.

Changing look transitions have been documented in other galaxies–most commonly in a class of active galaxies known as Seyfert galaxies. By definition, Seyfert galaxies all have a bright, active galactic nucleus, but Type 1 and Type 2 Seyfert galaxies differ in the amount of light they emit at specific wavelengths. According to Frederick, many astronomers suspect that the difference results from the angle at which astronomers view the galaxies.

Type 1 Seyfert galaxies are thought to face Earth head-on, giving an unobstructed view of their nuclei, while Type 2 Seyfert galaxies are tilted at an oblique angle, such that their nuclei are partially obscured by a donut-shaped ring of dense, dusty gas clouds. Thus, changing look transitions between these two classes present a puzzle for astronomers, since a galaxy’s orientation towards Earth is not expected to change.

Frederick and her colleagues’ new observations may call these assumptions into question.

© R. Buta (University of Alabama/Image enhancement: Jean-Baptiste Faur Spiral Seyfert Galaxy NGC 3081: Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

© R. Buta (University of Alabama/Image enhancement: Jean-Baptiste Faur
Spiral Seyfert Galaxy NGC 3081: Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

“We started out trying to understand changing look transformations in Seyfert galaxies. But instead, we found a whole new class of active galactic nucleus capable of transforming a wimpy galaxy to a luminous quasar,” said Suvi Gezari, an associate professor of astronomy at UMD, a co-director of JSI and a co-author of the research paper. “Theory suggests that a quasar should take thousands of years to turn on, but these observations suggest that it can happen very quickly. It tells us that the theory is all wrong. We thought that Seyfert transformation was the major puzzle. But now we have a bigger issue to solve.”

Frederick and her colleagues want to understand how a previously quiet galaxy with a calm nucleus can suddenly transition to a bright beacon of galactic radiation. To learn more, they performed follow-up observations on the objects with the Discovery Channel Telescope, which is operated by the Lowell Observatory in partnership with UMD, Boston University, the University of Toledo and Northern Arizona University. These observations helped to clarify aspects of the transitions, including how the rapidly transforming galactic nuclei interacted with their host galaxies.

“Our findings confirm that LINERs can, in fact, host active supermassive black holes at their centers,” Frederick said. “But these six transitions were so sudden and dramatic, it tells us that there is something altogether different going on in these galaxies. We want to know how such massive amounts of gas and dust can suddenly start falling into a black hole. Because we caught these transitions in the act, it opens up a lot of opportunities to compare what the nuclei looked like before and after the transformation.”

Unlike most quasars, which light up the surrounding clouds of gas and dust far beyond the galactic nucleus, the researchers found that only the gas and dust closest to the nucleus had been turned on. Frederick, Gezari and their collaborators suspect that this activity gradually spreads from the galactic nucleus–and may provide the opportunity to map the development of a newborn quasar.

“It’s surprising that any galaxy can change its look on human time scales. These changes are taking place much more quickly than we can explain with current quasar theory,” Frederick said. “It will take some work to understand what can disrupt a galaxy’s accretion structure and cause these changes on such short order. The forces at play must be very extreme and very dramatic.”

In addition to Frederick and Gezari, UMD-affiliated co-authors of the research paper include Adjunct Associate Professor of Astronomy Bradley Cenko, former Neil Gehrels Prize Postdoctoral Fellow Erin Kara and astronomy graduate student Charlotte Ward.

More information: Sara Frederick et al, A New Class of Changing-look LINERs, The Astrophysical Journal (2019). DOI: 10.3847/1538-4357/ab3a38

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Headline Image: © (Left; infrared & visible light imagery): ESA/Hubble, NASA and S. Smartt (Queen’s University Belfast); (Right; artist’s concept): NASA/JPL-Caltech

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ESPRESSO spectrograph confirms the existence of an earth-like planet near Proxima Centauri

The surface of Proxima b through the eyes of the artist ESO / M. Kornmesser

The ESPRESSO spectrograph confirmed the existence of the earth-like exoplanet Proxima b in the star closest to the Sun. Additional observations made by the tool made it possible to clarify its mass, as well as register a second signal, which theoretically can be explained by the presence of another planet. Accepted for publication at Astronomy & Astrophysics, the preprint is available at arXiv.org.

In 2016, astronomers reported the discovery of the planet at the red dwarf Proxima Centauri, the closest star to Earth, located about 4.2 light-years from Earth. The celestial body revolves around the star with a period of 11.2 days and is in the habitable zone – this means that the conditions on its surface allow the existence of liquid water.

The discovery of Proxima b was one of the most important milestones in exoplanetary astronomy in recent years, but the limited accuracy of the available measurements of radial velocity and the complexity of the simulation required confirmation of the existence of an earth-like planet.

An international group of astronomers used the new-generation spectrograph ESPRESSO, which is part of the VLT complex, to measure the radial velocity of a star with an accuracy of 30 centimeters per second. The data obtained were three times more accurate than the data of the HARPS spectrograph, an instrument of the same type, but of the previous generation, with the help of which the discovery was made. Combining ESPRESSO observations with past measurements showed that the mass of Proxima b is not less than 1.17 earth masses, which is less than the previous estimate of 1.27 earth masses.

In addition, scientists recorded an additional signal repeating with a period of 5.5 days, which so far they have not been able to explain. Hypothetically, it can come from the second planet: if the assumption is true, then its minimum mass is less than a third of the earth, and it is located at a distance of 0.03 astronomical units from Proxima Centauri (one astronomical unit is equal to the average distance from the Earth to the Sun).

In the past, researchers suspected the existence of another planet in the system – this time the super-earth, on which the year lasts about five years. It is five and a half times more massive than the Earth and may have rings similar to the rings of Saturn, but this discovery has not yet been confirmed.

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It’s time to worry. Planets switched to retrograde motion

© NASA / Tunc Tezel

In May, Venus, Saturn and Jupiter become retrograde – they change the direction of motion in the celestial sphere. Previously, it was considered a bad omen. In fact, in the solar system there is only one real retrograde – Venus. But the discovery of retrograde exoplanets was a complete surprise.

Copernicus explained everything

Even in ancient times, people noticed that planets moving in the heavens sometimes behave strangely, loop. Most of the year they follow from west to east (if they are farther from the Sun than the Earth) and suddenly turn around, back down. The moment when this happens is called standing.In 1514, Nicolaus Copernicus proved that the Earth is not the center of the universe, but together with other planets revolves around the Sun.

Each celestial body has its own orbit, and the retrograde movement that is visible to us is the result of their superposition. For example, Mars approaches the Earth every two years as closely as possible and, overtaking it, draws an s-shaped loop in the sky.

© NASA / Tunc Tezel

The path of Mars in the celestial sphere in the period from July 2005 to February 2006. It goes from west to east and at the moment of approaching the Earth makes a loop. For a couple of months his movement seems retrograde to us.

Venus and Uranus versus all

All planets in relation to the Earth for a short time move backward, but this is only an appearance. Real retrogrades do not physically rotate like the rest. In the solar system, it is only Venus. If we were above the north pole of Venus, we would see that it rotates clockwise around its axis. Earth and other planets are against.It is believed that planets form together with a star from one protoplanetary disk. In theory, their orbits should lie in the same plane, and the directions of rotation in the orbit and around the axis should coincide. Why Venus is not like this is not yet clear.

Although scientists note its strong similarity with the Earth – these planets are even called twins. One of the explanations is that the processes occurring in the bowels and atmosphere have slowed the rotation of Venus so much that it stopped at some point, and then began to spin in another direction.

The distant ice giant Uranus also looks like a retrograde. It lies on its side relative to the plane of its orbit, and pecks down the north pole, which makes Uranus seem to rotate clockwise. But if you put it normally, it will become normal. Scientists believe that billions of years ago, Uranus collided with a large cosmic body and turned over in space. Another hypothesis is that in the past the planet had a massive system of rings that caused resonance, rocked it and deployed.

General rules apply to planetary moons. For example, the Earth rotates counterclockwise, and so does the Moon around the Earth. But one of the 13 moons of Neptune – Triton – is “against the coat.” So, scientists conclude, Triton did not belong to Neptune, was an independent small body, until Neptune captured it from the Kuiper belt. By the way, Pluto, similar in composition to Triton, is also retrograde. In part, this contributed to its transfer to the category of dwarf planets.

© Illustration by RIA Novosti. NASA / JPLRetrograde motion of Triton. This is the only major satellite in the solar system that moves in orbit against the course of its planet.

Anomalies of hot jupiters

This is what our system is completely devoid of – planets that would move in orbits against the rotation of the Sun. For a long time, astronomers believed that this should be everywhere. But in 2009, they discovered the first exoplanet with a retrograde orbit at the star WASP-17 in the constellation Scorpio.WASP-17 b is the largest and least dense exoplanet known. Such gas giants are called hot jupiters.

Its retrograde intrigues scientists. Smadar Naoz from the Center for Interdisciplinary Research in Astrophysics at Northwestern University ( USA ) proposed a possible mechanism: the mutual influence of giant planets during migration closer to a star or a brown dwarf. But its implementation requires the coincidence of too many conditions, and this is unlikely. Nevertheless, the astrophysicist put forward a bold hypothesis that such retrograde jupiters are not uncommon – a quarter among those observed. However, the existence of the hot Jupiters themselves is still waiting for its explanation.

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A space object that changes the concept of the Universe is discovered: An unthinkable ancient galaxy

Photo: NRAO / AUI / NSF / S. Dagnello

Scientists at the Institute for Astronomy of the Max Planck Society in the UK announced the discovery of the oldest massive galaxy DLA0817g, which arose just 1.5 billion years after the Big Bang. It has a disk, which can change astronomers’ ideas about the mechanisms of galaxy formation. An article by astronomers is published in the journal Nature.

Researchers discovered the galaxy using the ALMA (Atacama Large Millimeter Array) radio telescope complex. This ancient object was named Wolf Disc – in honor of the astronomer Arthur Wolf. It has become the farthest spinning-disk galaxy of all detected so far, and its cosmological redshift is 4.26.

The light from it flew 12.2 billion years, but due to the expansion of the Universe, the galaxy is currently at a distance of 24.4 billion light years. The rotation occurs at a speed of 272 kilometers per second, which is comparable to the rotation speed of the Milky Way.

According to modern models, massive galaxies are formed from the mergers of smaller mass galaxies and clusters of hot gas. These collisions prevent the formation of disks characteristic of the Universe of this age.

Therefore, the existence of the Wolf Disc will force astronomers to reconsider the mechanisms of the appearance of such space objects. DLA0817g probably accumulated cold gas, but the question of how he managed to maintain a stable disk with such a large mass remains open.

Scientists also found that the star formation rate in the Wolf Disk is ten times higher than the star formation rate in the Milky Way. According to astronomers, he was one of the most productive galaxies in the early Universe.

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