“Enormous Ghost Galaxy” –Hidden In the Milky Way’s ‘Zone of Avoidance’



“Enormous Ghost Galaxy” –Hidden In the Milky Way’s ‘Zone of Avoidance’ (Weekend Feature)

Milky Way Galactic Center


An enormous ‘ghost’ galaxy, believed to be one of the oldest in the universe, was detected lurking on the outskirts of the Milky Way in November of 2018 by a team of astronomers who discovered the massive object when trawling through new data from the European Space Agency’s Gaia satellite. The object, named Antlia 2, avoided detection thanks to its extremely low density as well as a perfect hiding place in the Zone of Avoidance, behind the shroud of the Milky Way’s disc–a region full of dust and an overabundance of bright stars near the galactic center.

“This is a ghost of a galaxy,” said Gabriel Torrealba, an astrophysicist at Taiwan’s Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and the paper’s lead author. “Objects as diffuse as Ant 2 have simply not been seen before. Our discovery was only possible thanks to the quality of the Gaia data.” Gaia is able to dig into the Zone of Avoidance, he says, because it provides high-quality proper motions of stars behind the central disk of our Milky Way galaxy. That is, it is able to track stars as they move across the celestial sphere.

Optically, the Zone of Avoidance is like “trying to look through a velvet cloth—black as black can be,” says Thomas Dame, Director of the Radio Telescope Data Center at the Harvard-Smithsonian Center for Astrophysics and Senior Radio Astronomer at the Smithsonian Astrophysical Observatory. “In terms of tracing and understanding the spiral structure, essentially half of the Milky Way is terra incognito.”

“It’s the most Important thing in astrophysics”–the ‘Holy Grail’ of astronomy is to provide a clear perspective of our relationship to the physical universe. The map of our Milky Way galaxy is a part of that, a map that is still incomplete. Our solar system drifts between two spiral arms at its outer edges, some 27,000 light-years from its center. Beyond that, like the ancient sea-faring mariners, no space craft has ever traveled beyond the opaque central disk to turn back and take its picture.

“Monsters & Dragons?” –Mapping the Terra Incognito of Milky Way’s Unseen Far Side

“The zone of avoidance is basically the part of the sky obscured by the Milky Way’s disk as seen from the Earth,” said Torrealba. “The disk of the Milky Way has a lot of gas and stars, making it extremely crowded and complex.” But the team was able to use about a hundred old and metal-poor pulsating, so-called ‘RR Lyrae’ stars to probe inside and ultimately identify Antlia 2.

Optically, penetrating the Zone of Avoidance is like “trying to look through a velvet cloth—black as black can be,” says Thomas Dame, Director of the Radio Telescope Data Center at the Harvard-Smithsonian Center for Astrophysics and Senior Radio Astronomer at the Smithsonian Astrophysical Observatory. “In terms of tracing and understanding the spiral structure, essentially half of the Milky Way is terra incognito.”

“It’s the most Important thing in astrophysics”–the ‘Holy Grail’ of astronomy is to provide a clear perspective of our relationship to the physical universe. The map of our Milky Way galaxy is a part of that, a map that is still incomplete. Our solar system drifts between two spiral arms at its outer edges, some 27,000 light-years from its center. Beyond that, like the ancient sea-faring mariners, no space craft has ever traveled beyond the opaque central disk to turn back and take its picture.

Swarm of Faint Dwarf Galaxies Orbit the Milky Way –“Many More Hidden, Yet to Be Discovered”

“Compared to the rest of the 60 or so Milky Way satellites, Ant 2 is an oddball,” said co-author Matthew Walker, also from Carnegie Mellon University. “We are wondering whether this galaxy is just the tip of an iceberg, and the Milky Way is surrounded by a large population of nearly invisible dwarfs similar to this one.”


Antlia2 Dwarf Galaxy


Torrealba says that Antlia 2 is likeliest one of the oldest dwarf galaxies in the universe, but he and colleagues are still puzzled as to how it became so diffuse. “One possibility is that Antlia 2 was much more massive in the past, and as it fell into the Milky Way, it lost its mass to become more diffuse,” said Torrealba. One problem with this idea says Torrealba is that rather than grow, galaxies tend to shrink at the same time they lose stars.

Extreme Disk Galaxy Discovered –“Seven Times the Width of the Milky Way”

The object’s giant size, says astronomer Sergey Koposov at Carnegie Mellon University presents a puzzle, agreeing with Torrealba. “Normally, as galaxies lose mass to the Milky Way’s tides, they shrink, not grow.”

“Another possible explanation of the extraordinary appearance of Antlia 2,” Koposov wrote in an email to dailygalaxy.com, “is that there is something wrong with currently favored Cold Dark Matter theory that predicts that dark matter should be tightly packed in centers of galaxies. If dark matter distribution however is more fluffy, that can make it easier to form galaxies like Antlia 2,” he added.

Ant 2 is known as a dwarf galaxy. As structures emerged in the early Universe, dwarfs were the first galaxies to form, and so most of their stars are old, low-mass and metal-poor. But compared to the other known dwarf satellites of our Galaxy, Ant 2 is immense: it is as big as the Large Magellanic Cloud (LMC), and a third the size of the Milky Way itself.

What makes Ant 2 even more unusual is how little light it gives out. Compared to the LMC, another satellite of the Milky Way, Ant 2 is 10,000 times fainter. In other words, it is either far too large for its luminosity or far too dim for its size.

The ESA’s Gaia mission has produced the richest star catalog to date, including high-precision measurements of nearly 1.7 billion stars and revealing previously unseen details of our home Galaxy. Earlier in 2018, Gaia’s second data release made new details of stars in the Milky Way available to scientists worldwide.

The researchers behind the current study – from Taiwan, the UK, the US, Australia and Germany – searched the new Gaia data for Milky Way satellites by using RR Lyrae stars. These stars are old and metal-poor, typical of those found in a dwarf galaxy. RR Lyrae change their brightness with a period of half a day and can be located thanks to these well-defined pulses.

“RR Lyrae had been found in every known dwarf satellite, so when we found a group of them sitting above the Galactic disc, we weren’t totally surprised,” said co-author Vasily Belokurov from Cambridge’s Institute of Astronomy. “But when we looked closer at their location on the sky it turned out we found something new, as no previously identified object came up in any of the databases we searched through.”

The team contacted colleagues at the Anglo-Australian Telescope (AAT) in Australia, but when they checked the coordinates for Ant 2, they realized they had a limited window of opportunity to get follow-up data. They were able to measure the spectra of more than 100 red giant stars just before the Earth’s motion around the Sun rendered Ant 2 unobservable for months.

The spectra enabled the team to confirm that the ghostly object they spotted was real: all the stars were moving together. Ant 2 never comes too close to the Milky Way, always staying at least 40 kiloparsecs (about 130,000 light-years) away. The researchers were also able to obtain the galaxy’s mass, which was much lower than expected for an object of its size.

If it is impossible to puff the dwarf up by removing matter from it, then Ant 2 had to have been born huge. The team has yet to figure out the exact process that made Ant 2 so extended. While objects of this size and luminosity have not been predicted by current models of galaxy formation, recently it has been speculated that some dwarfs could be inflated by vigorous star formation. Stellar winds and supernova explosions would push away the unused gas, weakening the gravity that binds the galaxy and allowing the dark matter to drift outward as well.

“Even if star formation could re-shape the dark matter distribution in Ant 2 as it was put together, it must have acted with unprecedented efficiency,” said co-author Jason Sanders, also from Cambridge.

Alternatively, Ant 2’s low density could mean that a modification to the dark matter properties is needed. The currently favored theory predicts dark matter to pack tightly in the centers of galaxies. Given how fluffy the new dwarf appears to be, a dark matter particle which is less keen to cluster may be required.

The gap between Ant 2 and the rest of the Galactic dwarfs is so wide that this may well be an indication that some important physics is missing in the models of dwarf galaxy formation. Solving the Ant 2 puzzle may help researchers understand how the first structures in the early universe emerged.

The Daily Galaxy via Imperial College London

Did ‘Interstellar’ get it right about Black Holes?



Did ‘Interstellar’ get it right?



A supermassive black hole with millions to billions times the mass of our sun is seen in an undated NASA artist’s concept illustration.

The world will finally get to see how a black hole looks like.

The first-ever close-up of a black hole — the spaces at the center of every large galaxy — can be seen by the public at 9pm Beijing time today when six simultaneous press conferences are held in Shanghai, Taipei, Brussels, Chile’s Santiago, Tokyo and Washington.

The picture will have been captured by the Event Horizon Telescope, a network of eight radio telescopes scattered across the globe, thus creating a giant virtual telescope with a diameter equaling that of the Earth.

The EHT allows astronomers to clearly see an orange on the Moon.

The project’s researchers obtained the first data in April 2017 from the global network of telescopes.

The telescopes that collected that initial data are located in the US states of Arizona and Hawaii as well as Mexico, Chile, Spain and Antarctica. Since then, telescopes in France and Greenland have been added to the network.

The telescopes were trained on two supermassive black holes in very different corners of the universe to collect data. Sagittarius A*, in a mass of 4 million suns, is located at the center of the Milky Way, and another, unnamed, is located at the center of the neighboring Virgo A galaxy, weighing 1,500 times of Sagittarius A*.

The picture to be unveiled today is likely to zoom in on one or the other. The data collected by the far-flung telescope array still had to be collected and collated.

“The imaging algorithms we developed fill the gaps of data we are missing in order to reconstruct a picture of a black hole,” the team said on its website.

The EHT project involves more than 200 astronomers from across the world, including those from China.

The research will put to the test a scientific pillar — physicist Albert Einstein’s theory of general relativity, according to University of Arizona astrophysicist Dimitrios Psaltis, project scientist for the EHT. That theory, put forward in 1915, was intended to explain the laws of gravity and their relation to other natural forces.

Black holes live up to their name. Basically, it is a place in space that swallows almost everything.

A black hole’s event horizon, one of the most violent places in the universe, is the point of no return beyond which anything — stars, planets, gas, dust, all forms of electromagnetic radiation including light — gets sucked in irretrievably.

For us, black holes are “dark stars.” So how do astronomers find black holes?

When black holes tear up nearby stars and swallow things in the space, they will emit great energy, generating bright light and massive radiation, through collision and friction.

That lead astronomers to the locations of black holes.

How do black holes look like?

No one knows, at least not until we discover it today.


Over the years, they have been depicted in many ways in the movies, but it is widely regarded that its image in the hit Hollywood movie “Interstellar” is the closest to the real thing.

Similar to the shape of Saturn, a star with rings, the black hole as depicted in “Interstellar” is very massive and rapidly spinning black with a glowing ring of matter encircling it.

The image was created after consultations with physicist and Nobel Laureate Kip Thorne of the California Institute of Technology.

Einstein’s theory, if correct, should allow for an extremely accurate prediction of the size and shape of a black hole.

“The shape of the shadow will be almost a perfect circle in Einstein’s theory,” Psaltis said. “If we find it to be different than what the theory predicts, then we go back to square one and we say, ‘Clearly, something is not exactly right.’”

Breakthrough observations in 2015 that earned the scientists involved a Nobel Prize used gravitational wave detectors to track two black holes smashing together.

As they merged, ripples in the curvatures of time-space created a unique, and detectable, signature.

“Einstein’s theory of general relativity says that this is exactly what should happen,” said Paul McNamara, an astrophysicist at the European Space Agency and an expert on black holes.

But those were tiny black holes — only 60 times more massive than the Sun — compared with either of the ones under the gaze of the EHT.

“Maybe the ones that are millions of times more massive are different — we just don’t know yet,” said McNamara.

How big is a black hole?

The diameter of a black hole depends on its mass but it is always double what we call the Schwarzschild radius. If the sun were to shrink to a singularity point, the Schwarzschild radius would be 3 kilometers and the diameter would be 6. For Earth, the diameter would be 18 millimeters, or about three quarters of an inch. The event horizon of the black hole at the center of the Milky Way, Sagittarius A*, measures about 24 million kilometers across.

What will the image look like?

The Event Horizon Telescope is not looking at the black hole per se, but the material it has captured. It won’t be a big disk in high resolution like in the Hollywood movie “Interstellar.” But we might see a black core with a bright ring — the accretion disk — around it. The light from behind the black hole gets bent like a lens. No matter what the orientation of the disk, you will see it as a ring because of the black hole’s strong gravity. Visually, it will look very much like an eclipse.

How is the image generated?

Rather than having one telescope that is 100 meters across, they have lots of telescopes with an effective diameter of 12,000km — the diameter of Earth. The data is recorded with very high accuracy, put onto hard disks, and shipped to a central location where the image is reconstructed digitally. This is very, very long baseline interferometry — over the entire surface of the Earth.

Eight planets found orbiting distant star, NASA says



Eight planets found orbiting distant star, NASA says

The galaxy explained

Story highlights

  • For the first time, eight planets have been found orbiting Kepler-90
  • It is tied with our solar system for a star hosting the most known planets

(CNN) For the first time, eight planets have been found orbiting a distant star, Kepler-90, 2,545 light-years from Earth in the Draco constellation, NASA announced Thursday. It is the first star known to support as many planets as are orbiting our own sun, and researchers believe that this is the first of many to come.

Researchers had known that seven planets were orbiting the star. But Google Artificial Intelligence — which enables computers to “learn” — looked at archival data obtained by NASA’s planet-hunting Kepler telescope and uncovered the eighth planet.
With the idea of eventually differentiating among exoplanets, Christopher Shallue, senior software engineer at Google AI in California, and Andrew Vanderburg, astronomer and NASA Sagan postdoctoral fellow at the University of Texas, Austin, trained a computer how to differentiate between images of cats and dogs.
They refined their approach to identify exoplanets in Kepler data based on the change in light when a planet passed in front of its star. The neural network learned to identify these by using signals that had been vetted and confirmed in Kepler’s planet catalog. Ninety-six percent of the time, it was accurate.
Since launching in 2009, Kepler has watched more than 150,000 stars in one part of the sky to determine exoplanet candidates, based on the slight dimming of stars as potential planets pass across them. Kepler gathered a dataset of 35,000 possible signals indicating planets. In order to help find weaker signals of potential planets that researchers had missed, the neural network was trained to look for weak signals in star systems that were known to support multiple planets.
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“Machine learning really shines in situations where there is so much data that humans can’t search it for themselves,” Shallue said.
The new planet has been dubbed Kepler-90i. It’s not a hospitable environment. It’s small, “sizzling” hot and rocky, whirling around its star every 14.4 days. In our solar system, the closest planet to the sun, Mercury, has an orbit of 88 days.
“The Kepler-90 star system is like a mini version of our solar system. You have small planets inside and big planets outside, but everything is scrunched in much closer,” Vanderburg said.
Although Kepler-90 is a sun-like star, the planets are all bunched together in tight orbits around it — the same distance that Earth is from the sun.

“Just as we expected, there are exciting discoveries lurking in our archived Kepler data, waiting for the right tool or technology to unearth them,” said Paul Hertz, director of NASA’s Astrophysics Division in Washington. “This finding shows that our data will be a treasure trove available to innovative researchers for years to come.”
Researchers also announced that they had uncovered a sixth planet in the Kepler-80 system, Kepler-80g, which is similar in size to Earth. It also has an orbit of 14.4 days. The star is cooler and redder than our sun, and all of the planets orbit very tightly around it. Five of the six planets form a resonant chain, in which they are locked in orbit by mutual gravity. The Kepler-80 system is stable, as the previously discovered seven-planet TRAPPIST-1 system has proven to be.
To date, Kepler has observed 2,525 confirmed exoplanets.
“These results demonstrate the enduring value of Kepler’s mission,” said Jessie Dotson, Kepler’s project scientist at NASA’s Ames Research Center in California. “New ways of looking at the data — such as this early-stage research to apply machine learning algorithms — promises to continue to yield significant advances in our understanding of planetary systems around other stars. I’m sure there are more firsts in the data waiting for people to find them.”
Missions launching in 2018, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will enable further and closer study of planet candidates identified by Kepler.
Compared with Kepler, TESS will use a similar transit method for observing planets when they pass in front of their parent stars. Though Kepler looked at one portion of the sky for stars that were farther away for a longer time, TESS will observe the entire sky and focus on the brightest and closest stars, each for 30 days.
The James Webb Space Telescope is capable of observing large exoplanets and detecting starlight filtered through their atmospheres, which will enable scientists to determine the atmospheric composition and analyze them for gases that can create a biological ecosystem.
The K2 mission, which launched in 2014, is extending Kepler’s legacy to new parts of the sky and new fields of study, adding to NASA’s “arc of discovery.” It has enough fuel to keep identifying candidates until summer 2018. It’s helping bridge the gap between Kepler and TESS as far as identifying targets for the James Webb Space Telescope to observe.