Galaxy Orbits In The Local Supercluster

A team of astronomers from Maryland, Hawaii, Israel and France has produced the most detailed map ever of the orbits of galaxies in our extended local neighborhood, showing the past motions of almost 1,400 galaxies within 100 million light years of the Milky Way.

The team reconstructed the galaxies’ motions from 13 billion years in the past to the present day. The main gravitational attractor in the mapped area is the Virgo Cluster, with 600 trillion times the mass of the Sun, 50 million light years from us. Over a thousand galaxies have already fallen into the Virgo Cluster, while in the future all galaxies that are currently within 40 million light years of the cluster will be captured. Our Milky Way galaxy lies just outside this capture zone. However, the Milky Way and Andromeda galaxies, each with 2 trillion times the mass of the Sun, are destined to collide and merge in 5 billion years.

“For the first time, we are not only visualizing the detailed structure of our Local Supercluster of galaxies but we are seeing how the structure developed over the history of the universe. An analogy is the study of the current geography of the Earth from the movement of plate tectonics,” said co-author Brent Tully from the University of Hawaii’s Institute for Astronomy.

These dramatic merger events are only part of a larger show. There are two overarching flow patterns within this volume of the universe. All galaxies in one hemisphere of the region — including our own Milky Way — are streaming toward a single flat sheet. In addition, essentially every galaxy over the whole volume is flowing, as a leaf would in a river, toward gravitational attractors at far greater distances.

Representations of the orbits can be seen in a video and, alternatively, with an interactive model. With the interactive model, a viewer can pan, zoom, rotate and pause/activate the time evolution of movement along orbits. The orbits are shown in a reference frame that removes the overall expansion of the universe. What we are seeing are the deviations from cosmic expansion caused by the interactions of local sources of gravity.

Black Holes’ Magnetism Surprisingly Wimpy

Black holes are famous for their muscle: an intense gravitational pull known to gobble up entire stars and launch streams of matter into space at almost the speed of light.

It turns out the reality may not live up to the hype.

In a paper published today in the journal Science, University of Florida scientists have discovered these tears in the fabric of the universe have significantly weaker magnetic fields than previously thought.

A 40-mile-wide black hole 8,000 light years from Earth named V404 Cygni yielded the first precise measurements of the magnetic field that surrounds the deepest wells of gravity in the universe. Study authors found the magnetic energy around the black hole is about 400 times lower than previous crude estimates.

The measurements bring scientists closer to understanding how black holes’ magnetism works, deepening our knowledge of how matter behaves under the most extreme conditions — knowledge that could broaden the limits of nuclear fusion power and GPS systems.

The measurements also will help scientists solve the half-century-old mystery of how “jets” of particles traveling at nearly the speed of light shoot out of black holes’ magnetic fields, while everything else is sucked into their abysses, said study co-author Stephen Eikenberry, a professor of astronomy in UF’s College of Liberal Arts and Sciences.

“The question is, how do you do that?” Eikenberry said. “Our surprisingly low measurements will force new constraints on theoretical models that previously focused on strong magnetic fields accelerating and directing the jet flows. We weren’t expecting this, so it changes much of what we thought we knew.”

Study authors developed the measurements from data collected in 2015 during a black hole’s rare outburst of jets. The event was observed through the lens mirror of the 34-foot Gran Telescopio Canarias, the world’s largest telescope, co-owned by UF and located in Spain’s Canary Islands, with the help of its UF-built infrared camera named CIRCE (Canarias InfraRed Camera Experiment).

Smaller jet-producing black holes, like the one observed for the study, are the rock stars of galaxies. Their outbursts occur suddenly and are short-lived, said study lead author Yigit Dalilar and co-author Alan Garner, doctoral students in UF’s astronomy department. The 2015 outbursts of V404 Cygni lasted only a couple of weeks. The previous time the same black hole had a similar episode was in 1989.

“To observe it was something that happens once or twice in one’s career,” Dalilar said. “This discovery puts us one step closer to understanding how the universe works.”

Two Super-Earths Around Red Dwarf K2-18

New research using data collected by the European Southern Observatory (ESO) has revealed that a little-known exoplanet called K2-18b could well be a scaled-up version of Earth.

Just as exciting, the same researchers also discovered for the first time that the planet has a neighbor.

“Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally exciting,” says lead author Ryan Cloutier, a PhD student in U of T Scarborough’s Centre for Planet Science, U of T’s Department of Astronomy and Astrophysics, and Université de Montréal Institute for research on exoplanets (iREx).

Both planets orbit K2-18, a red-dwarf star located about 111 light years away in the constellation Leo. When the planet K2-18b was first discovered in 2015, it was found to be orbiting within the star’s habitable zone, making it an ideal candidate to have liquid surface water, a key element in harbouring conditions for life as we know it.

The data set used by the researchers came from the High Accuracy Radial Velocity Planet Searcher (HARPS) using the ESO’s 3.6m telescope at La Silla Observatory, in Chile. HARPS allows for measurements of radial velocities of stars, which can be affected by the presence of nearby planets, to be taken with the highest accuracy currently available. The instrument makes it possible to detect very small planets orbiting those stars.

In order to figure out whether K2-18b was a scaled-up version of Earth (mostly rock), or a scaled-down version of Neptune (mostly gas), researchers had to first figure out the planet’s mass, using radial velocity measurements taken with HARPS.

“If you can get the mass and radius, you can measure the bulk density of the planet and that can tell you what the bulk of the planet is made of,” says Cloutier.

After using a machine-learning approach to figure out the mass measurement, Cloutier and his team were able to determine the planet is either a mostly rocky planet with a small gaseous atmosphere — like Earth, but bigger — or a mostly water planet with a thick layer of ice on top of it.

“With the current data, we can’t distinguish between those two possibilities,” he says. “But with the James Webb Space Telescope (JWST) we can probe the atmosphere and see whether it has an extensive atmosphere or it’s a planet covered in water.”

The JWST, which will be launched in 2019, will be instrumental in collecting a range of data for studying the solar system, early universe and exoplanets.

“There’s a lot of demand to use this telescope, so you have to be meticulous in choosing which exoplanets to look at,” says René Doyon, a co-author on the paper who is also the principal investigator for NIRISS, the Canadian Space Agency instrument on board JWST.

“K2-18b is now one of the best targets for atmospheric study, it’s going to the near top of the list.”

It was while looking through the data of K2-18b that Cloutier noticed something unusual. In addition to a signal occurring every 39 days from the rotation of K2-18, and one taking place every 33 days from the orbit of K2-18b, he noticed a different signal occurring every nine days.

“When we first threw the data on the table we were trying to figure out what it was. You have to ensure the signal isn’t just noise, and you need to do careful analysis to verify it, but seeing that initial signal was a good indication there was another planet,” Cloutier says.

Cloutier collaborated with an international team of researchers from the Observatoire Astronomique de l’Universite? de Gene?ve, the Institute for research on exoplanets (iREx), Universite? de Grenoble, U of T Scarborough, and Universidade do Porto.

While the newly described planet K2-18c is closer to its star, and probably too hot to be in the habitable zone, like K2-18b it also appears to be a Super-Earth meaning it has a mass similar to Earth. Cloutier, who had set the goal of discovering a new exoplanet within his PhD, considers himself very lucky to have discovered it in this dataset.

“It wasn’t a eureka moment because we still had to go through a checklist of things to do in order to verify the data. Once all the boxes were checked it sunk in that, wow, this actually is a planet.”

Gravitational Waves Could Shed Light On The Origin Of Black Holes

A new study published in Physical Review Letters outlines how scientists could use gravitational wave experiments to test the existence of primordial black holes, gravity wells formed just moments after the Big Bang that some scientists have posited could be an explanation for dark matter.

“We know very well that black holes can be formed by the collapse of large stars, or as we have seen recently, the merger of two neutron stars,” said Savvas Koushiappas, an associate professor of physics at Brown University and coauthor of the study with Avi Loeb from Harvard University. “But it’s been hypothesized that there could be black holes that formed in the very early universe before stars existed at all. That’s what we’re addressing with this work.”

The idea is that shortly after the Big Bang, quantum mechanical fluctuations led to the density distribution of matter that we observe today in the expanding universe. It’s been suggested that some of those density fluctuations might have been large enough to result in black holes peppered throughout the universe. These so-called primordial black holes were first proposed in the early 1970s by Stephen Hawking and collaborators but have never been detected — it’s still not clear if they exist at all.

The ability to detect gravitational waves, as demonstrated recently by the Laser Interferometer Gravitational-Wave Observatory (LIGO), has the potential to shed new light on the issue. Such experiments detect ripples in the fabric of spacetime associated with giant astronomical events like the collision of two black holes. LIGO has already detected several black hole mergers, and future experiments will be able to detect events that happened much further back in time.

“The idea is very simple,” Koushiappas said. “With future gravitational wave experiments, we’ll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we’ll know that those black holes are not of stellar origin.”

Cosmologists measure how far back in time an event occurred using redshift — the stretching of the wavelength of light associated with the expansion of the universe. Events further back in time are associated with larger redshifts. For this study, Koushiappas and Loeb calculated the redshift at which black hole mergers should no longer be detected assuming only stellar origin.

They show that at a redshift of 40, which equates to about 65 million years after the Big Bang, merger events should be detected at a rate of no more than one per year, assuming stellar origin. At redshifts greater than 40, events should disappear altogether.

“That’s really the drop-dead point,” Koushiappas said. “In reality, we expect merger events to stop well before that point, but a redshift of 40 or so is the absolute hardest bound or cutoff point.”

A redshift of 40 should be within reach of several proposed gravitational wave experiments. And if they detect merger events beyond that, it means one of two things, Koushiappas and Loeb say: Either primordial black holes exist, or the early universe evolved in a way that’s very different from the standard cosmological model. Either would be very important discoveries, the researchers say.

For example, primordial black holes fall into a category of entities known as MACHOs, or Massive Compact Halo Objects. Some scientists have proposed that dark matter — the unseen stuff that is thought to comprise most of the mass of the universe — may be made of MACHOs in the form of primordial black holes. A detection of primordial black holes would bolster that idea, while a non-detection would cast doubt upon it.

The only other possible explanation for black hole mergers at redshifts greater than 40 is that the universe is “non-Gaussian.” In the standard cosmological model, matter fluctuations in the early universe are described by a Gaussian probability distribution. A merger detection could mean matter fluctuations deviate from a Gaussian distribution.

“Evidence for non-Gaussianity would require new physics to explain the origin of these fluctuations, which would be a big deal,” Loeb said.

The rate at which detections are made past a redshift of 40 — if indeed such detections are made — should indicate whether they’re a sign of primordial black holes or evidence for non-Gaussianity. But a non-detection would present a strong challenge to those ideas.

Giant Black Hole Pair Photobombs Andromeda Galaxy

It seems like even black holes can’t resist the temptation to insert themselves unannounced into photographs. A cosmic photobomb found as a background object in images of the nearby Andromeda galaxy has revealed what could be the most tightly coupled pair of supermassive black holes ever seen.

Astronomers made this remarkable discovery using X-ray data from NASA’s Chandra X-ray Observatory and optical data from ground-based telescopes, Gemini-North in Hawaii and the Caltech’s Palomar Transient Factory in California.

This unusual source, called LGGS J004527.30+413254.3 (J0045+41 for short), was seen in optical and X-ray images of Andromeda, also known as M31. Until recently, scientists thought J0045+41 was an object within M31, a large spiral galaxy located relatively nearby at a distance of about 2.5 million light years from Earth. The new data, however, revealed that J0045+41 was actually at a much greater distance, around 2.6 billion light years from Earth.

“We were looking for a special type of star in M31 and thought we had found one,” said Trevor Dorn-Wallenstein of the University of Washington in Seattle, WA, who led the paper describing this discovery. “We were surprised and excited to find something far stranger!”

Even more intriguing than the large distance of J0045+41 is that it likely contains a pair of giant black holes in close orbit around each other. The estimated total mass for these two supermassive black holes is about two hundred million times the mass of our Sun.

Previously, a different team of astronomers had seen periodic variations in the optical light from J0045+41, and, believing it to be a member of M31, classified it as a pair of stars that orbited around each other about once every 80 days.

The intensity of the X-ray source observed by Chandra revealed this original classification was incorrect. Rather, J0045+41 had to be either a binary system in M31 containing a neutron star or black hole that is pulling material from a companion—the sort of system Dorn-Wallenstein was originally searching for in M31—or a much more massive and distant system that contains at least one rapidly growing supermassive black hole.
However, a spectrum from the Gemini-North telescope taken by the University of Washington team showed that J0045+41 must host at least one supermassive black hole and allowed the researchers to estimate the distance. The spectrum also provided possible evidence that a second black hole was present in J0045+41 and moving at a different velocity from the first, as expected if the two black holes are orbiting each other.

The team then used optical data from the Palomar Transient Factory to search for periodic variations in the light from J0045+41. They found several periods in J0045+41, including ones at about 80 and 320 days. The ratio between these periods matches that predicted by theoretical work on the dynamics of two giant black holes orbiting each other.

“This is the first time such strong evidence has been found for a pair of orbiting giant black holes,” said co-author Emily Levesque of the University of Washington.

The researchers estimate that the two putative black holes orbit each other with a separation of only a few hundred times the distance between the Earth and the Sun. This corresponds to less than one hundredth of a light year. By comparison, the nearest star to our Sun is about four light years away.

Such a system could be formed as a consequence of the merger, billions of years earlier, of two galaxies that each contained a supermassive black hole. At their current close separation, the two black holes are inevitably being drawn closer together as they emit gravitational waves.

“We’re unable to pinpoint exactly how much mass each of these black holes contains,” said co-author John Ruan, also of the University of Washington. “Depending on that, we think this pair will collide and merge into one black hole in as little as 350 years or as much as 360,000 years.”

If J0045+41 indeed contains two closely orbiting black holes it will be emitting gravitational waves, however the signal would not be detectable with LIGO and Virgo. These ground-based facilities have detected the mergers of stellar-mass black holes weighing no more than about 60 Suns and, very recently, one between two neutron stars.

“Supermassive black hole mergers occur in slow motion compared to stellar-mass black holes”, said Dorn-Wallenstein. “The much slower changes in the gravitational waves from a system like J0045+41 can be best detected by a different type of gravitational wave facility called a Pulsar Timing Array.”

MUSE Probes Uncharted Depths Of Hubble Ultra Deep Field

The MUSE HUDF Survey team, led by Roland Bacon of the Centre de recherche astrophysique de Lyon (CNRS/Université Claude Bernard Lyon 1/ENS de Lyon), France, used MUSE (Multi Unit Spectroscopic Explorer/ to observe the Hubble Ultra Deep Field (heic0406/, a much-studied patch of the southern constellation of Fornax (The Furnace). This resulted in the deepest spectroscopic observations ever made; precise spectroscopic information was measured for 1600 galaxies, ten times as many galaxies as has been painstakingly obtained in this field over the last decade by ground-based telescopes.

The original HUDF images were pioneering deep-field observations with the NASA/ESA Hubble Space Telescope published in 2004. They probed more deeply than ever before and revealed a menagerie of galaxies dating back to less than a billion years after the Big Bang. The area was subsequently observed many times by Hubble and other telescopes, resulting in the deepest view of the Universe to date. Now, despite the depth of the Hubble observations, MUSE has — among many other results — revealed 72 galaxies never seen before in this very tiny area of the sky.

Roland Bacon takes up the story: “MUSE can do something that Hubble can’t — it splits up the light from every point in the image into its component colours to create a spectrum. This allows us to measure the distance, colours and other properties of all the galaxies we can see — including some that are invisible to Hubble itself.”

The MUSE data provides a new view of dim, very distant galaxies, seen near the beginning of the Universe about 13 billion years ago. It has detected galaxies 100 times fainter than in previous surveys, adding to an already richly observed field and deepening our understanding of galaxies across the ages.

The survey unearthed 72 candidate galaxies known as Lyman-alpha emitters that shine only in Lyman-alpha light. Current understanding of star formation cannot fully explain these galaxies, which just seem to shine brightly in this one colour. Because MUSE disperses the light into its component colours these objects become apparent, but they remain invisible in deep direct images such as those from Hubble.

“MUSE has the unique ability to extract information about some of the earliest galaxies in the Universe — even in a part of the sky that is already very well studied,” explains Jarle Brinchmann, lead author of one of the papers describing results from this survey, from the University of Leiden in the Netherlands and the Institute of Astrophysics and Space Sciences at CAUP in Porto, Portugal. “We learn things about these galaxies that is only possible with spectroscopy, such as chemical content and internal motions — not galaxy by galaxy but all at once for all the galaxies!”

Another major finding of this study was the systematic detection of luminous hydrogen halos around galaxies in the early Universe, giving astronomers a new and promising way to study how material flows in and out of early galaxies.

Many other potential applications of this dataset are explored in the series of papers, and they include studying the role of faint galaxies during cosmic reionisation (starting just 380,000 years after the Big Bang), galaxy merger rates when the Universe was young, galactic winds, star formation as well as mapping the motions of stars in the early Universe.

“Remarkably, these data were all taken without the use of MUSE’s recent Adaptive Optics Facility upgrade. The activation of the AOF after a decade of intensive work by ESO’s astronomers and engineers promises yet more revolutionary data in the future,” concludes Roland Bacon.

Traces Of Life On Nearest Exoplanets May Be Hidden In Equatorial Trap

New simulations show that the search for life on other planets may well be more difficult than previously assumed, in research published today in the journal Monthly Notices of the Royal Astronomical Society. The study indicates that unusual air flow patterns could hide atmospheric components from telescopic observations, with direct consequences for formulating the optimal strategy for searching for (oxygen-producing) life such as bacteria or plants on exoplanets.

Current hopes of detecting life on planets outside of our own Solar System rest on examining the planet’s atmosphere to identify chemical compounds that may be produced by living beings. Ozone — a variety of oxygen — is one such molecule, and is seen as one of the possible tracers that may allow us to detect life on another planet from afar.

In Earth’s atmosphere, this compound forms the ozone layer that protects us from the Sun’s harmful UV radiation. On an alien planet, ozone could be one piece in the puzzle that indicates the presence of oxygen-producing bacteria or plants.

But now researchers, led by Ludmila Carone of the Max Planck Institute for Astronomy in Germany, have found that these tracers might be better hidden than we previously thought. Carone and her team considered some of the nearest exoplanets that have the potential to be Earth-like: Proxima b, which is orbiting the star nearest to the Sun (Proxima Centauri), and the most promising of the TRAPPIST-1 family of planets, TRAPPIST-1d.

These are examples of planets that orbit their host star in 25 days or fewer, and as a side effect have one side permanently facing their star, and the other side permanently facing away. Modelling the flow of air within the atmospheres of these planets, Carone and her colleagues found that this unusual day-night divide can have a marked effect on the distribution of ozone across the atmosphere: at least for these planets, the major air flow may lead from the poles to the equator, systematically trapping the ozone in the equatorial region.

Carone says: “Absence of traces of ozone in future observations does not have to mean there is no oxygen at all. It might be found in different places than on Earth, or it might be very well hidden.”

Such unexpected atmospheric structures may also have consequences for habitability, given that most of the planet would not be protected against ultraviolet (UV) radiation. “In principle, an exoplanet with an ozone layer that covers only the equatorial region may still be habitable,” Carone explains. “Proxima b and TRAPPIST-1d orbit red dwarfs, reddish stars that emit very little harmful UV light to begin with. On the other hand, these stars can be very temperamental, and prone to violent outbursts of harmful radiation including UV.”

The combination of advances in modelling and much better data from telescopes like the James Webb Space Telescope is likely to lead to significant progress in this exciting field. “We all knew from the beginning that the hunt for alien life will be a challenge,” says Carone. “As it turns out, we are only just scratching the surface of how difficult it really will be.”