Follow us on:

Posts Tagged ‘Astronomy & Astrophysics’

Astronomy & Astrophysics

TAU-led team discovers new way black holes are “fed”

These “giant monsters” were observed suddenly devouring gas in their surroundings

Supermassive black holes weigh millions to billions times more than our sun and lie at the center of most galaxies. A supermassive black hole several million times the mass of the sun is situated in the heart of our very own Milky Way.

Despite how commonplace supermassive black holes are, it remains unclear how they grow to such enormous proportions. Some black holes constantly swallow gas in their surroundings, some suddenly swallow whole stars. But neither theory independently explains how supermassive black holes can “switch on” so unexpectedly and keep growing so fast for a long period.

A new Tel Aviv University-led study published today in Nature Astronomy finds that some supermassive black holes are triggered to grow, suddenly devouring a large amount of gas in their surroundings.

Following the light

In February 2017, the All Sky Automated Survey for Supernovae discovered an event known as AT 2017bgt. This event was initially believed to be a “star swallowing” event, or a “tidal disruption” event, because the radiation emitted around the black hole grew more than 50 times brighter than what had been observed in 2004.

However, after extensive observations using a multitude of telescopes, a team of researchers led by Dr. Benny Trakhtenbrot and Dr. Iair Arcavi, both of TAU’s Raymond & Beverly Sackler School of Physics and Astronomy, concluded that AT 2017bgt represented a new way of “feeding” black holes.

“The sudden brightening of AT 2017bgt was reminiscent of a tidal disruption event,” says Dr. Trakhtenbrot. “But we quickly realized that this time there was something unusual. The first clue was an additional component of light, which had never been seen in tidal disruption events.”

Dr. Arcavi, who led the data collection, adds, “We followed this event for more than a year with telescopes on Earth and in space, and what we saw did not match anything we had seen before.”

The observations matched the theoretical predictions of another member of the research team, Prof. Hagai Netzer, also of Tel Aviv University.

“We had predicted back in the 1980s that a black hole swallowing gas from its surroundings could produce the elements of light seen here,” says Prof. Netzer. “This new result is the first time the process was seen in practice.”

Mysterious re-activation 

Astronomers from the U.S., Chile, Poland and the U.K. took part in the observations and analysis effort, which used three different space telescopes, including the new NICER telescope installed on board the International Space Station.

One of the ultraviolet images obtained during the data acquisition frenzy turned out to be the millionth image taken by the Neil Gehrels Swift Observatory — an event celebrated by NASA, which operates this space mission.

The research team identified two additional recently reported events of black holes “switched on,” which share the same emission properties as AT 2017bgt. These three events form a new and tantalizing class of black hole re-activation.

“We are not yet sure about the cause of this dramatic and sudden enhancement in the black holes’ feeding rate,” concludes Dr. Trakhtenbrot. “There are many known ways to speed up the growth of giant black holes, but they typically happen during much longer timescales.”

“We hope to detect many more such events, and to follow them with several telescopes working in tandem,” says Dr. Arcavi. “This is the only way to complete our picture of black hole growth, to understand what speeds it up, and perhaps finally solve the mystery of how these giant monsters form.”

Continue Reading

Astronomy & Astrophysics

Astronomers Discover Giant Relic of Disrupted “Tadpole” Galaxy

Discovery illuminates how and why galaxies disappear, say Tel Aviv University researchers

Remains of a dwarf galaxy almost containing mostly stars (the victim) disrupted by a pair of much larger and more massive galaxies (white “smudges” near the center of the tadpole). Created as the victim’s stars were scattered the galaxy pair into the head. Lagging stars form the long tail.

Tel Aviv — A team of astronomers from Israel, the United States and Russia have identified a disrupted galaxy resembling a giant tadpole, complete with an elliptical head and a long, straight tail, about 300 million light years away from Earth. The galaxy is 1 million light-years long from end to end, 10 times longer than the Milky Way.

“We have found a giant, exceptional relic of a disrupted galaxy,” says Dr. Noah Brosch of The Florence and George Wise Observatory at Tel Aviv University’s School of Physics and Astronomy, who led the research for the study.

When galaxies are disrupted and disappear, their stars are either incorporated into more massive galaxies or are ejected into intergalactic space. “What makes this object extraordinary is that the tail alone is almost 500,000 light-years long,” says Prof. R. Michael Rich of UCLA. “If it were at the distance of the Andromeda galaxy, which is about 2.5 million light-years from Earth, it would reach a fifth of the way to our own Milky Way.”

Drs. Brosch and Rich collaborated on the study with Dr. Alexandr Mosenkov of St. Petersburg University and Dr. Shuki Koriski of TAU’s Florence and George Wise Observatory and School of Physics and Astronomy. The results were published in the Monthly Notices of the Royal Astronomical Society.

According to the study, the giant “tadpole” was produced by the disruption of a small, previously invisible dwarf galaxy containing mostly stars. When the gravitational force of two visible galaxies pulled on stars in this vulnerable galaxy, the stars closer to the pair formed the “head” of the tadpole. Stars lingering in the victim galaxy formed the “tail.”

“The extragalactic tadpole contains a system of two very close ‘normal’ disk galaxies, each about 40,000 light-years across,” says Dr. Brosch. “Together with other nearby galaxies, the galaxies form a compact group.” The galaxy is part of a small group of galaxies called HCG098 that will merge into a single galaxy in the next billion years.

Such compact galaxy groups were identified in 1982 by astronomer Paul Hickson, who published a catalog of 100 such groups. The Hickson Compact Groups examine environments with high galaxy densities that are not at the core of a “cluster” of galaxies (clusters contain thousands of galaxies themselves). The “tadpole galaxy” is listed as No. 98 in the Hickson Compact Group catalog.

“In compact group environments, we believe we can study ‘clean’ examples of galaxy-galaxy interactions, learn how matter is transferred between the members, and how newly accreted matter can modify and influence galaxy growth and development,” says Dr. Brosch.

For the research, the scientists collected dozens of images of the targets, each exposed through a wide filter that selects red light while virtually eliminating extraneous light pollution. “We used a relatively small, 70-cm telescope at the Wise Observatory and an identical telescope in UCLA, both of which were equipped with state-of-the-art CCD cameras,” says Dr. Brosch. The two telescopes are collaborating on a project called the Halos and Environments of Nearby Galaxies Survey.

The new study is part of a long-term project at TAU’s Florence and George Wise Observatory, which explores the skies at low light levels to detect the faintest details of studied galaxies.

Continue Reading

Astronomy & Astrophysics

First tangible proof that “dark matter” exists

Prof. Rennan Barkana has managed to shed light on one of astronomy’s biggest mysteries

A team of astronomers led by Prof. Judd Bowman of Arizona State University unexpectedly stumbled upon “dark matter,” the most mysterious building block of outer space, while attempting to detect the earliest stars in the universe through radio wave signals, according to a study published this week in Nature.

The idea that these signals implicate dark matter is based on a second Nature paper published this week, by Prof. Rennan Barkana of the Raymond & Beverly Sackler Faculty of Exact Sciences at Tel Aviv University, which suggests that the signal is proof of interactions between normal matter and dark matter in the early universe. According to Prof. Barkana, the discovery offers the first direct proof that dark matter exists and that it is composed of low-mass particles.

The signal, recorded by a novel radio telescope called EDGES, dates to 180 million years after the Big Bang.

What the universe is made of

“Dark matter is the key to unlocking the mystery of what the universe is made of,” says Prof. Barkana, Head of the Department of Astrophysics at TAU’s School of Physics and Astronomy. “We know quite a bit about the chemical elements that make up the earth, the sun and other stars, but most of the matter in the universe is invisible and known as ‘dark matter.’ The existence of dark matter is inferred from its strong gravity, but we have no idea what kind of substance it is. Hence, dark matter remains one of the greatest mysteries in physics.

“To solve it, we must travel back in time. Astronomers can see back in time, since it takes light time to reach us. We see the sun as it was eight minutes ago, while the immensely distant first stars in the universe appear to us on earth as they were billions of years in the past.”

Prof. Bowman and colleagues reported the detection of a radio wave signal at a frequency of 78 megahertz. The width of the observed profile is largely consistent with expectations, but they also found it had a larger amplitude (corresponding to deeper absorption) than predicted, indicating that the primordial gas was colder than expected.

Prof. Barkana suggests that the gas cooled through the interaction of hydrogen with cold, dark matter.

“Tuning in” to the early universe

“I realized that this surprising signal indicates the presence of two actors: the first stars, and dark matter,” says Prof. Barkana. “The first stars in the universe turned on the radio signal, while the dark matter collided with the ordinary matter and cooled it down. Extra-cold material naturally explains the strong radio signal.”

Physicists expected that any such dark matter particles would be heavy, but the discovery indicates low-mass particles. Based on the radio signal, Prof. Barkana argues that the dark-matter particle is no heavier than several proton masses. “This insight alone has the potential to reorient the search for dark matter,” says Prof. Barkana.

Once stars formed in the early universe, their light was predicted to have penetrated the primordial hydrogen gas, altering its internal structure. This would cause the hydrogen gas to absorb photons from the cosmic microwave background, at the specific wavelength of 21 cm, imprinting a signature in the radio spectrum that should be observable today at radio frequencies below 200 megahertz. The observation matches this prediction except for the unexpected depth of the absorption.

 Prof. Barkana predicts that the dark matter produced a very specific pattern of radio waves that can be detected with a large array of radio antennas. One such array is the SKA, the largest radio telescope in the world, now under construction. “Such an observation with the SKA would confirm that the first stars indeed revealed dark matter,” concludes Prof. Barkana.

Continue Reading

Astronomy & Astrophysics

Gravitational waves: a new way to observe the universe

TAU utilizes Nobel-winning research to expand our understanding of matter and space

On August 17, 2017, scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in Louisiana and Washington and at the Virgo detector in Italy detected the first “ripples in space,” or gravitational waves, produced by the merger of two ancient remnants of stars known as neutron stars.

The 2017 Nobel Prize in Physics was awarded to the creators of the LIGO instrument and its detection of gravitational waves. Scientists at Tel Aviv University are racing to use results from the LIGO experiments to expand our understanding of the universe, with the new discovery appearing today in Science and Nature. An additional TAU study is appearing in the Astrophysical Journal.

“This is a milestone in the growing effort by scientists worldwide to unlock the mysteries of the universe and of earth,” says Prof. Ehud Nakar of TAU’s Raymond and Beverly Sackler School of Physics and Astronomy, who together with his graduate student Ore Gottlieb led the theoretical analysis for the new studies on the discovery appearing today in Science and Nature.

The studies were led by Dr. Yair Arcavi, who joins TAU’s School of Physics and Astronomy next year from UC Santa Barbara, in collaboration with Prof. Dovi Poznanski, Prof. Dan Maoz and their students at TAU’s School of Physics and Astronomy.

Building on Einstein

The existence of gravitational waves was first predicted by Albert Einstein a century ago. They afford insight into an event that took place in a galaxy 120 million light years away and provide valuable information on the evolution of exploding neutron stars, as well as the origin of gold, uranium and other heavy metals on earth.

“It is difficult to exaggerate the importance of this discovery,” says Prof. Poznanksi. “Until recently, we could observe the universe only through light waves that reached us. This new ability to study gravitational waves is analogous to a sense of touch. It’s as though we now have the ability to explore the universe through both sight and touch.”

“This discovery has allowed astronomers to combine gravitational waves with light and produce a detailed model of the emission for the first time. This introduces a new era in astronomy,” says Gottlieb.

A neutron star forms when a star much bigger and brighter than the sun exhausts its thermonuclear fuel supply and explodes into a violent supernova. The explosion of neutron stars, which are made almost entirely of neutrons, was detected by multiple telescopes across the electromagnetic spectrum, from gamma rays and visible light to radio waves.

“This is only the beginning,” Prof. Maoz notes. “We expect many surprising discoveries in the coming years.”

Continue Reading

Astronomy & Astrophysics

Can you hear a shooting star?

A new study explains why some people can hear sounds when they see a meteor passing

Have you ever wondered what a shooting star sounds like? There have been records for centuries of people claiming they could hear a sound when they saw a meteor cross the sky. A new study from Prof. Colin Price, the Head of The Porter School of Environmental Studies, proposes a new theory for how humans could see and hear a shooting star at the same time.

Meteors release lots of energy when they disintegrate and burn up in the Earth’s atmosphere (what we commonly think of as a “shooting star”).  According to Prof. Price, shooting stars “produce radio waves that travel at the speed of light, together with the light we see, to the observer”.

While the radio waves are electromagnetic waves that cannot be heard, they can be converted into sound waves that we can hear by any electricity conducting material (metal fence, radio speaker, hair, spectacles and so on) giving us the sounds associated with meteors, simultaneously with the visible light we see.

Phantom sounds

However, despite the anecdotal evidence of people hearing sounds when they see meteors in the sky, there are few explanations for how meteors produce electromagnetic waves in the first place. Prof. Price, along with Prof. Michael Kelley of Cornell University, have developed a new model that can explain how the phenomenon occurs.

To hear a sound, the radio waves have to be in a specific frequency range, similar the frequencies our ear can hear, between 20 Hz – 20 kHz.  This is known as the very low frequency (VLF) range. Prof. Price and Prof. Kelley theorized that the size of a meteor and the speed with which it travels controls the frequency of the radio waves it produces.

A meteor in motion ionizes the air around it, splitting it into heavy ions and lighter, negatively charged electrons. That separation of positive and negative charges in the meteor’s wake produces a large electric field that drives an electrical current. And it’s that current that launches the VLF radio waves.

Prof. Price believes this model may also explain the reports of “clapping” sounds that sometimes accompany auroras, known also as “northern lights”. These sounds have been reported for centuries by people living in the most northern parts of the Earth, in places like Canada and Greenland. 

Continue Reading

Subscribe to our newsletter!

(You agree that Canadian Friends of Tel Aviv University may collect, use and disclose your personal data which you have provided in this form, for providing marketing material that you have agreed to receive, in accordance with our data protection policy.)

CFTAU Ontario & Western Canada
3130 Bathurst Street, Suite, 214, Toronto, ON | M6A 2A1 | Phone: 416.787.9930
Email: toronto@cftau.ca

CFTAU Ottawa, Quebec and Atlantic Canada
6900 Boulevard Décarie, Suite 3480, Montreal, QC | H3X 2T8 | Phone: 514.344.3417
Email: montreal@cftau.ca

Terms and ConditionsPrivacy • © 2017 CFTAU