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Like a massive, dormant volcano, the Milky Way's central black hole appears to be a sleeping monster. Black holes are regions of spacetime where gravity is so strong that “what goes into them does not come out,” says Avery Broderick, a faculty member at the Perimeter Institute. As the name implies, black holes are intrinsically dark, with no light or matter able to escape once they have passed the threshold of no return known as the event horizon. But as black holes feast on the surrounding gas and stars, their accretion disks can shine and produce extraordinary energy. They can even outshine their host galaxies.

In December of 2015, the international Event Horizon Telescope research team measured for the first time the magnetic fields that contribute to black hole growth. The ETH, a linked array of millimeter-wavelength telescopes that spans the globe and is set to take the highest-resolution images in the history of astronomy. When trained on the black hole at the center of our galaxy, Sagittarius A*, it can see the structural details in the accretion flow that surrounds the black hole horizon.

For the first time, astronomers have detected evidence of black-hole-scale magnetic fields near the black hole at the center of our galaxy. Were these magnetic fields not there, “a lot of theoretical astrophysics would have to go back to the drawing board,” says Broderick, jointly appointed at the University of Waterloo. The discovery, published in the journal Science, moves the understanding of how black holes grow from the realm of theoretical speculation to the territory of empirical fact, Broderick says.

Broderick was part of a collaboration that discovered high levels of polarization in the radio emission from Sagittarius A*, the bright radio source believed to be the astronomical manifestation of the 4.5-million-solar-mass black hole.

The current observations are from only three of the sites in the global EHT array, comparable to having just a handful of pixels of the larger picture that will eventually be produced. Nevertheless, these few pixels are already writing the preface to the coming revolution in our understanding of black holes. Researchers are able to begin the process of putting our best current ideas of what is happening near the black hole to the test.

It will also shed light on the reverse process, whereby some black holes are capable of launching outflows of energy and material at nearly the speed of light, extending the black hole's impact to intergalactic scales. Decades of theoretical work, including enormous computer simulations, painted a picture of how strong magnetic fields near the black hole horizon contribute to the processes that enable a black hole to grow. But now, with the data from the EHT, scientists can begin to see how these processes work in practice.

The radio emission in Sagittarius A* is generated by high-energy electrons zipping around magnetic field lines. This produces highly polarized emission on microscopic scales, tied to the local orientation of the magnetic field, so the polarization traces the structure of the magnetic fields. Detecting high polarization on the size of the black hole horizon at Sagittarius A* does two things. First, it verifies that magnetic fields are there and that they must be ordered. Second, it provides a measurement of the typical size of these magnetic structures.

There is much more to come. Taking images of the accretion disk around Sagittarius A*, which has an event horizon that is smaller than the orbit of Mercury, is a feat akin to trying to image a grapefruit on the moon. But the EHT array should be able to accomplish that. “There are now enough telescopes in the array, in principle, to make images in the next couple of years,” Broderick adds.

Those images will enable astrophysicists to transform our understanding of how black holes grow, how they interact with their surroundings, and even the nature of gravity. By studying the details of the cosmic “traffic jam” caused by gas as it rushes headlong towards the black hole, researchers will be able to check if Albert Einstein's theory of general relativity, one of the pillars of modern physics, holds up in the extreme gravity conditions around black holes.

The Chandra Observatory image above provides a panoramic X-ray view extending 400 light years by 900 light years shows that, even at this distance from the center of the Galaxy, conditions are getting crowded, and the energy level is increasing dramatically. Supernova remnants (SNR 0.9-0.1, probably the X-ray Thread, and Sagittarius A East), bright binary X-ray sources containing a black hole or a neutron star (the 1E sources), and hundreds of unnamed point-like sources due to neutron stars or white dwarfs light up the region. The massive stars in the Arches and other star clusters (the DB sources) will soon explode to produce more supernovas, neutron stars, and black holes.

Infrared and radio telescopes have also revealed giant star-forming molecular clouds (Sagittarius A, B1, B2 and C, and the cold gas cloud near the Radio Arc), the edges of which are glowing with X-rays because of heating from nearby supernovas.

'If, however, Sagittarius A* was more active in the past,' Christopher van Eldik explains, 'then it could indeed be responsible for the bulk of today's galactic cosmic rays that are observed on earth.' If true, this would dramatically influence the century-old debate on the origins of galactic cosmic rays, as the theory that their components are primarily accelerated to PeV energies by remnants of supernovae - shock waves that occur after the explosion of massive stars - would have to be revised to take this into account.

"We have wondered why the Milky Way's black hole appears to be a slumbering giant," observed Tatsuya Inui of Kyoto University in Japan. "But now we realize that the black hole was far more active in the past. Perhaps it's just resting after a major outburst." Tatsuya Inui is part of a team that used results from Japan's Suzaku and ASCA X-ray satellites, NASA's Chandra X-ray Observatory, and the European Space Agency's XMM-Newton X-ray Observatory, to determine the history of our black hole.

It turns out that, approximately 300 years ago, Sagittarius A* let loose, expelling a massive energy flare. Data taken from 1994 to 2005 revealed that clouds of gas near the central black hole, known as Sagittarius B2, brightened and faded quickly in X-ray light. The X-rays were emanating from just outside the black hole, created by the buildup of matter piling up outside the black hole, which subsequently heats up and expels X-rays.

These pulses of X-ray take 300 years to traverse the distance between Sagittarius A* and Sagittarius B2, so that when we witness something happening in the cloud, it is responding to something that happened 300 years ago. Amazingly for us, in a rare occurrence of perfect cosmic timing, a region in Sagittarius B2, only 10 light-years across varied dramatically in brightness. "By observing how this cloud lit up and faded over 10 years, we could trace back the black hole's activity 300 years ago," says team member Katsuji Koyama of Kyoto University.

The Weekend Feature

The Daily Galaxy via Perimeter Institute for Theoretical Physics

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NASA's Hubble researchers say that future Earths are more likely to appear inside giant galaxy clusters (such as the massive cluster galaxy-cluster-macs-j0717 above) and also in dwarf galaxies, which have yet to use up all their gas for building stars and accompanying planetary systems. By contrast, our Milky Way galaxy has used up much more of the gas available for future star formation.

Earth came early to the party in the evolving universe. According to the new theoretical study, when our solar system was born 4.6 billion years ago only eight percent of the potentially habitable planets that will ever form in the universe existed. And, the party won't be over when the sun burns out in another 6 billion years. The bulk of those planets -- 92 percent -- have yet to be born. This conclusion is based on an assessment of data collected by NASA's Hubble Space Telescope and the prolific planet-hunting Kepler space observatory.

A big advantage to our civilization arising early in the evolution of the universe is our being able to use powerful telescopes like Hubble to trace our lineage from the big bang through the early evolution of galaxies. The observational evidence for the big bang and cosmic evolution, encoded in light and other electromagnetic radiation, will be all but erased away 1 trillion years from now due to the runaway expansion of space. Any far-future civilizations that might arise will be largely clueless as to how or if the universe began and evolved.

"Our main motivation was understanding the Earth's place in the context of the rest of the universe," said study author Peter Behroozi of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, "Compared to all the planets that will ever form in the universe, the Earth is actually quite early."

Looking far away and far back in time, Hubble has given astronomers a "family album" of galaxy observations that chronicle the universe's star formation history as galaxies grew. The data show that the universe was making stars at a fast rate 10 billion years ago, but the fraction of the universe's hydrogen and helium gas that was involved was very low. Today, star birth is happening at a much slower rate than long ago, but there is so much leftover gas available that the universe will keep cooking up stars and planets for a very long time to come.

"There is enough remaining material [after the big bang] to produce even more planets in the future, in the Milky Way and beyond," added co-investigator Molly Peeples of STScI.

Kepler's planet survey indicates that Earth-sized planets in a star's habitable zone, the perfect distance that could allow water to pool on the surface, are ubiquitous in our galaxy. Based on the survey, scientists predict that there should be 1 billion Earth-sized worlds in the Milky Way galaxy at present, a good portion of them presumed to be rocky. That estimate skyrockets when you include the other 100 billion galaxies in the observable universe.

This leaves plenty of opportunity for untold more Earth-sized planets in the habitable zone to arise in the future. The last star isn't expected to burn out until 100 trillion years from now. That's plenty of time for literally anything to happen on the planet landscape.

The results appeared in the Monthly Notices of the Royal Astronomical Society.

The Weekend Feature

The Daily Galaxy via NASA/Goddard Space Flight Center

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Researchers at Bar Ilan University and the Interdisciplinary Center in Herzliya, both in Israel, have developed new technology that allows tiny bots to release drugs into the body controlled by human thought alone. The test involved a man using his thoughts to activate nano robots inside a cockroach.

The Israeli team believe the bots could help in controlled release of drugs over time. Led by Dr Ido Bachelet of Bar Ilan University, scientists demonstrated how to control this process with human brainwaves. Using a computer algorithm, they trained the system to detect when a person's brain was under strain from doing mental arithmetic. The team then placed a fluorescent drug in the bots and injected them into various cockroaches that were placed inside an electromagnetic coil.

Wearing an EEG cap (which measures brain activity, the human subject was then tasked with solving mental arithmetic puzzles. By looking at when the fluorescent was released in the cockroaches, scientists were able to conclude their experiment had worked.

“As a proof of principle we demonstrate activation of DNA robots to cause a cellular effect inside the insect Blaberus discoidalis, by a cognitively straining task,” researchers wrote in the journal Public Library of Science One. “This technology enables the online switching of a bioactive molecule on and off in response to a subject's cognitive state.”

The researchers believe the technology could be used to treat disorders such as schizophrenia, depression and ADHD.

The Daily Galaxy via Bar Ilan University and The Interdisciplinary Centre

Image credit: auricmedia.net

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Sir Roger Penrose, a mathematical physicist at Oxford University, has asked "what right do we have to claim, as some might, that human beings are the only inhabitants of our planet blessed with an actual ability to be "aware"? It is hard to see how one could begin to develop a quantum-theoretical description of brain action when one might well have to regard the brain as "observing itself" all the time! Beneath all this technicality is the feeling that it is indeed "obvious" that the conscious mind cannot work like a computer, even though much of what is involved in mental activity might do so.

“I think consciousness will remain a mystery. I have a much easier time imagining how we understand the Big Bang than I have imagining how we can understand consciousness," said theoretical physicist Edward Wittten of the Institute for Advanced Study at Princeton, who has been compared to Einstein and Newton.

In recent years, human consciousness has emerged as one of the hottest new fields in biology, similar to string theory in physics or the search for extraterrestrial life in astronomy. No longer the purview of philosophers and mystics, consciousness is now attracting the attention of scientists from across a variety of different fields, each, it seems, with their own theories about what consciousness is and how it arises from the brain.

Penrose believes that if a "theory of everything" is ever developed in physics to explain all the known phenomena in the universe, it should at least partially account for consciousness. Penrose believes that quantum mechanics, the rules governing the physical world at the subatomic level, might play an important role in consciousness as shown in the video below.

Recently, Edward Witten, a theoretical physicist and professor of mathematical physics at the Institute for Advanced Study in Princeton, New Jersey, has joined philosopher Colin McGinn and Penrose who argue that ultimately, consciousness is unsolvable.

"I think consciousness will remain a mystery, says Witten. "Yes, that's what I tend to believe. I tend to think that the workings of the conscious brain will be elucidated to a large extent. Biologists and perhaps physicists will understand much better how the brain works. But why something that we call consciousness goes with those workings, I think that will remain mysterious. I have a much easier time imagining how we understand the Big Bang than I have imagining how we can understand consciousness."

In a recent video interview with journalist Wim Kayzer (below), Witten, says he is pessimistic about the prospects for a scientific explanation of consciousness.

Today's Most Popular

The Daily Galaxy via blogs.scientificamerican.com, Kavli Institute, nytimes.com

Image credit: With thanks to esawdilis.com

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NASA: "Black Holes are Dark Matter Concentrators"

“Very soon after its discovery, we realized this galaxy had to be more than meets the eye. It has so few stars that it would quickly be ripped apart unless something was holding it together,” said Yale University astronomer Pieter van Dokkum.

Using the world's most powerful telescopes, an international team of astronomers has found a massive galaxy that consists almost entirely of dark matter. The galaxy, Dragonfly 44, is located in the nearby Coma constellation and had been overlooked until last year because of its unusual composition: It is a diffuse “blob” about the size of the Milky Way, but with far fewer stars.

Van Dokkum's team was able to get a good look at Dragonfly 44 thanks to the W.M. Keck Observatory and the Gemini North telescope (below), both in Hawaii. Astronomers used observations from Keck, taken over six nights, to measure the velocities of stars in the galaxy. They used the 8-meter Gemini North telescope to reveal a halo of spherical clusters of stars around the galaxy's core, similar to the halo that surrounds our Milky Way galaxy.

Star velocities are an indication of the galaxy's mass, the researchers noted. The faster the stars move, the more mass its galaxy will have.

“Amazingly, the stars move at velocities that are far greater than expected for such a dim galaxy. It means that Dragonfly 44 has a huge amount of unseen mass,” said co-author Roberto Abraham of the University of Toronto.

Scientists initially spotted Dragonfly 44 with the Dragonfly Telephoto Array, a telescope invented and built by van Dokkum and Abraham.

The image below shows the dark galaxy Dragonfly 44. The image on the left is from the Sloan Digital Sky Survey. Only a faint smudge is visible. The image on the right is a long exposure with the Gemini telescope, revealing a large, elongated object. Dragonfly 44 is very faint for its mass and consists almost entirely of dark matter. (Images by Pieter van Dokkum, Roberto Abraham, Gemini, Sloan Digital Sky Survey)

Dragonfly 44's mass is estimated to be 1 trillion times the mass of the Sun, or 2 tredecillion kilograms (a 2 followed by 42 zeros), which is similar to the mass of the Milky Way. However, only one-hundredth of 1% of that is in the form of stars and “normal” matter. The other 99.99% is in the form of dark matter — a hypothesized material that remains unseen but may make up more than 90% of the universe.

The researchers note that finding a galaxy composed mainly of dark matter is not new; ultra-faint dwarf galaxies have similar compositions. But those galaxies were roughly 10,000 times less massive than Dragonfly 44.

“We have no idea how galaxies like Dragonfly 44 could have formed,” said Abraham. “The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we're just guessing.”

Van Dokkum, the Sol Goldman Family Professor of Astronomy and Physics at Yale, added: “Ultimately what we really want to learn is what dark matter is. The race is on to find massive dark galaxies that are even closer to us than Dragonfly 44, so we can look for feeble signals that may reveal a dark matter particle.”

The Daily Galaxy via Yale University

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