From Ethan Siegel: “Antimatter Mystery Likely Due To Pulsars, Not Dark Matter”

From Ethan Siegel
Jan 2

NASA’s Fermi Satellite has constructed the highest resolution, high-energy map of the Universe ever created. Without space-based observatories such as this one, we could never learn all that we have about the Universe, nor could we even accurately measure the gamma-ray sky. (NASA/DOE/FERMI LAT COLLABORATION)

NASA/Fermi LAT

NASA/Fermi Gamma Ray Space Telescope

For years, astronomers have been puzzled by an excess of antimatter particles. Unfortunately, dark matter is probably not the solution.

When you look out at the Universe, what you see is only a tiny portion of what’s actually out there. If you examine the Universe solely with what’s perceptible to your eyes, you’ll miss out on a whole slew of information that exists in wavelengths of light that are invisible to us. From the highest-energy gamma rays to the lowest-energy radio waves, the electromagnetic spectrum is enormous, with visible light representing just a tiny sliver of what’s out there.

However, there’s an entirely different method to measure the Universe: to collect actual particles and antiparticles, a science known as cosmic ray astronomy. For more than a decade, astronomers have seen a signal of cosmic ray positrons — the antimatter counterpart of the electron — that they’ve struggled to explain. Could it be humanity’s best clue towards solving the dark matter mystery? A new study says no, it’s probably just pulsars. [Physical Review D]

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

Here’s why.

Cosmic rays produced by high-energy astrophysics sources can reach any object in the Solar System, and appear to permeate our local region of space omnidirectionally. When they collide with Earth, they strike atoms in the atmosphere, creating particle and radiation showers at the surface, while direct detectors in space, above the atmosphere, can measure the original particles directly. (ASPERA COLLABORATION / ASTROPARTICLE ERANET)

There are a great many things in the Universe that are known to create positrons, the antimatter counterpart of electrons. Whenever you have a high-enough energy collision between two particles, there’s a certain amount of energy that will be available with the potential to create new particle-antiparticle pairs. If that available energy is greater than the equivalent mass of the new particle(s) you want to create, as defined by Einstein’s E = mc2, there’s a finite probability of generating those new particles.

There are all sorts of high-energy processes that can lead to this type of energy becoming available, including particles accelerated by black holes, high-energy protons colliding with the galactic disk, or particles accelerated in the vicinity of neutron stars. Based on the known physics and astrophysics of the Universe, we know that a certain amount of positrons must be generated irrespective of any new physics.

Two bubbles of high-energy signatures are evidence that electron/positron annihilation is occurring, likely powered by processes at the galactic center. Here on Earth, more positrons than can be explained by conventional physics are seen via direct cosmic ray experiments, putting forth the exciting possibility that dark matter might be the cause of both that excess and the galactic center gamma rays. (NASA’S GODDARD SPACE FLIGHT CENTER)

However, we also expect that there is some new physics out there, because of the overwhelming astrophysical evidence for dark matter. While the true nature of dark matter will remain a mystery until the particle (or at least one of the particles) responsible for it is detected directly, many dark matter scenarios exist where not only is dark matter its own antiparticle, but that dark matter annihilations will also produce electron-positron pairs.

Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

Fritz Zwicky from http:// palomarskies.blogspot.com

Coma cluster via NASA/ESA Hubble

Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

LSST telescope, The Vera Rubin Survey Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

Dark Matter Research

Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

Scientists studying the cosmic microwave background [CMB]hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

[caption id="attachment_73741" align="alignnone" width="632"] CMB per ESA/Planck

Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

Dark Matter Particle Explorer China

DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

LBNL LZ Dark Matter project at SURF, Lead, SD, USA

Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

Whenever you have multiple possible physical explanations for what could cause an observable phenomenon, the key to telling which one matches reality is to tease out differences between the explanations. In particular, positrons due to dark matter should experience a cutoff at specific energies (corresponding to the mass of the dark matter particles), while positrons generated by conventional astrophysics should fall off more gradually.

NASA/AMS02 device on the ISS

In 2011, the Alpha Magnetic Spectrometer experiment (AMS-02) was launched with the goal of further investigating this mystery. After arriving at the International Space Station aboard the final mission of the Space Shuttle Endeavor, it was quickly set up and began sending data back to Earth within 3 days. During its operational phase, it collected and measured more than ten billion cosmic ray particles per year.

What’s remarkable about AMS-02 is that it didn’t just measure cosmic ray particles, but was able to sort them both by type and by energy, providing us with an unprecedented set of data to evaluate whether the positrons appeared to be due to dark matter or not. At low energies, the data matched the predictions of cosmic rays colliding with the interstellar medium, but at higher energies, something else was clearly at play.

If the AMS-02 experiment had not experienced any failures or required any repairs, it would have collected sufficient data to distinguish between pulsars (blue) or annihilating dark matter (red) as the source of the excess positrons. Either way, collisions of cosmic rays with the interstellar medium can only explain the low-energy signature, with another explanation required for the high-energy signatures. (AMS COLLABORATION)

However, that’s not a slam dunk for dark matter by any means. At higher energies, it’s also possible that pulsars, which accelerate matter particles to incredible energies through a combination of their gravitational and electromagnetic forces, could produce a peaked excess of positrons at high energies.

Although AMS-02 sees evidence (at 4-sigma, or 99.99% confidence) that there’s a peak and then a falloff in the observed energies of positrons, its sensitivity and event rate peters out at exactly the types of energies that would enable us to differentiate between a positron signal arising from pulsars versus one arising from annihilating dark matter. With spacewalks currently ongoing to attempt to repair AMS-02 and bring it back online to continue its observations, it may eventually collect enough data to discern, on its own, whether pulsars or dark matter provide the best fit to the data.

The Vela pulsar, like all pulsars, is an example of a neutron star corpse. The gas and matter surrounding it is quite common, and is capable of providing fuel for the pulsing behavior of these neutron stars. Matter-antimatter pairs, as well as high-energy particles, are produced in copious amounts by neutron stars, offering up the possibility that they, and not dark matter, are responsible for the excess signals observed by AMS-02. (NASA/CXC/PSU/G.PAVLOV ET AL.)

However, there’s more than one way to tell these two scenarios apart, as positrons produced by pulsars should also generate an additional signal that falls well outside the measurements that AMS-02 or any cosmic ray experiment could detect: gamma rays.

If pulsars truly generate the positrons that could be responsible for the signal that cosmic ray experiments are seeing, then a significant fraction of those positrons will have the misfortune of colliding with electrons in the interstellar medium long before they arrive at our cosmic ray detectors. When positrons collide with electrons, they annihilate, with each reaction producing two gamma rays with a very specific energy signature: 511 keV of energy, the rest-energy equivalent of an electron’s (or positron’s) mass, also obtained from Einstein’s E = mc2.

The production of matter/antimatter pairs (left) from pure energy is a completely reversible reaction (right), with matter/antimatter annihilating back to pure energy. When a photon is created and then destroyed, it experiences those events simultaneously, while being incapable of experiencing anything else at all. If you operate in the center-of-momentum (or center-of-mass) rest frame, particle/antiparticle pairs (including two photons) will zip off at 180 degree angles to one another, with energies equal to the rest-mass equivalent of each of the particles, as defined by Einstein’s E = mc². (DMITRI POGOSYAN / UNIVERSITY OF ALBERTA)

However, pulsars should theoretically be able to accelerate these electrons and positrons up to extraordinarily high energies: energies that even the world’s most powerful terrestrial particle accelerator, the Large Hadron Collider, struggles to reach. When photons — even normal-energy starlight — interact with these ultra-relativistic (near light-speed) particles, they can get boosted to extraordinary energies through a process known as inverse Compton scattering.

Based on physical parameters like the properties of the pulsar, the matter in the pulsar’s vicinity, the electrons and positrons generated, and the amount of starlight present nearby, a specific energy spectrum will be created for the photons generated from this process. Sum them all up for all of the nearby, relevant pulsars, and your gamma ray signature might indicate that pulsars, and not dark matter, cause this positron excess.

Particles traveling near light speed can interact with starlight and boost it to gamma-ray energies. This animation shows the process, known as inverse Compton scattering. When light ranging from microwave to ultraviolet wavelengths collides with a fast-moving particle, the interaction boosts it to gamma rays, the most energetic form of light. (NASA / GSFC)

About 800 light-years away, incredibly close by astronomical standards, one of the brightest gamma-ray pulsars in the entire sky can be found: Geminga. It was only discovered in 1972, and had its nature revealed in 1991, when the ROSAT mission measured evidence for a neutron star spinning at a rate of 4.2 revolutions-per-second.

Geminga. Patrizia Caraveo (INAF/IASF), Milan

ROSAT X-ray satellite built by DLR , with instruments built by West Germany, the United Kingdom and the United States

Fast-forward to the present day, where NASA’s Fermi Large Area Telescope — with enormously improved spatial and energy resolution — is now the world’s most sophisticated gamma ray observatory. By subtracting out the gamma ray signal arising from cosmic rays colliding with interstellar gas clouds, the remnant signal from starlight interacting with accelerated electrons and positrons could be revealed.

When a team of researchers led by Mattia di Mauro analyzed the Fermi data [Physical Review D], what they saw was spectacular: an energy-dependent signal that, at its largest, spanned some 20 degrees in the sky at the exact energies that AMS-02 was most sensitive to.

This model of Geminga’s gamma-ray halo shows how the emission changes at different energies, a result of two effects. The first is the pulsar’s rapid motion through space over the decade Fermi’s Large Area Telescope has observed it. Second, lower-energy particles travel much farther from the pulsar before they interact with starlight and boost it to gamma-ray energies. This is why the gamma-ray emission covers a larger area at lower energies. (NASA’S GODDARD SPACE FLIGHT CENTER/M. DI MAURO)

Explaining this glow, which decreases in size as Fermi looks at progressively higher energies, fit the models perfectly by leveraging a combination of inverse Compton scattering with the pulsar’s motion through interstellar space. According to Fiorenza Donato, coauthor on the recent Fermi study that measured gamma rays from Geminga Physical Review D [above],
Lower-energy particles travel much farther from the pulsar before they run into starlight, transfer part of their energy to it, and boost the light to gamma rays. This is why the gamma-ray emission covers a larger area at lower energies. Also, Geminga’s halo is elongated partly because of the pulsar’s motion through space.

The measurement of the gamma rays from Geminga alone suggests that this one pulsar could be responsible for as much as 20% of the high-energy positrons seen by the AMS-02 experiment.

This animation shows a region of the sky centered on the pulsar Geminga. The first image shows the total number of gamma rays detected by Fermi’s Large Area Telescope at energies from 8 to 1,000 billion electron volts (GeV) — billions of times the energy of visible light — over the past decade. By removing all bright sources, astronomers discovered the pulsar’s faint, extended gamma-ray halo, concluding that this one pulsar could be responsible for up to 20% of the positrons detected by the AMS-02 experiment. (NASA/DOE/FERMI LAT COLLABORATION)

Whenever there’s an unexplained phenomenon that we’ve measured or observed, it presents a tantalizing possibility to scientists: that perhaps there’s something new at play beyond what’s presently known. We know there are mysteries about our Universe that require new physics at some level — mysteries like dark matter, dark energy, or the cosmic matter-antimatter asymmetry — whose ultimate solution has yet to be discovered.

However, we cannot claim evidence for a new discovery until everything that represents what’s already known is quantified and accounted for. By factoring in the effect of pulsars, the positron excess observed by the Alpha Magnetic Spectrometer collaboration may turn out to be explicable entirely by conventional high-energy astrophysics, with no need for dark matter. Right now, it appears that pulsars may be responsible for 100% of the observed excess, requiring scientists to go back to the drawing board for a direct signal that reveals our Universe’s elusive dark matter.

See the full article here .

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

From Discover Magazine: “Using Gamma Rays, Scientists Map Out 21 New Constellations”

From Discover Magazine

October 19, 2018
Chelsea Gohd

The Godzilla constellation in the gamma-ray sky — a new set of constellations based off of gamma-ray emissions observed with NASA’s Fermi Gamma-ray Space Telescope. (Credit: NASA)

NASA/Fermi LAT

NASA/Fermi Gamma Ray Space Telescope

Gamma-Ray Sky

For countless years, humans have gazed up at the sky and made sense of the stars by finding shapes in them — constellations of heroes, animals, and well-worn tales. Now, to celebrate the 10th mission year of NASA’s Fermi Gamma-ray Space Telescope, scientists have used the telescope to develop a new set of constellations that correspond with gamma-ray emissions [Future post].

Gamma rays are the most powerful in the electromagnetic spectrum, and they’re typically only produced by very powerful objects. Supermassive black holes at the center of galaxies emit gamma rays, and gamma rays can also spring from explosive gamma-ray bursts, pulsars, the debris of supernova explosions, and more. The Fermi telescope has spent the last decade scanning the sky to compile list of gamma ray sources in the observable universe. That’s given them an array of points, similar to the stars we see shining in the visible spectrum.

In what is known as the “gamma-ray sky,” scientists have devised constellations inspired by many of the same things that inspired the starlight constellations our ancestors gazed at.

The “original” constellations primarily fall into three categories: myths and legends, meaningful topics and common creatures and items, NASA Goddard’s Elizabeth Ferrara, who led the constellation project, explained in a teleconference. The Fermi constellations from the gamma-ray sky are also derived from three categories: modern legends, team partners, and Fermi science. To make sure they didn’t look too much like stars, the team behind these constellations used artificial color to distinguish them.

Familiar Shapes

There are 21 Fermi constellations, including the Hulk (created from a gamma-ray mishap), Godzilla, the Starship Enterprise from “Star Trek: The Next Generation”, the TARDIS from “Doctor Who”, gamma-ray bursts, dark lightning, spider pulsars. Important landmarks from partner nations show up as well: Mt. Fuji for Japan, the Colosseum to represent Italy and more. The constellations even include a Saturn V rocket to represent Huntsville, Alabama where the gamma-ray burst monitor team is centered.

(Credit: NASA)
The Godzilla constellation in the gamma-ray sky — a new set of constellations based off of gamma-ray emissions observed with NASA’s Fermi Gamma-ray Space Telescope. (Credit: NASA)
Gamma-Ray Sky

For countless years, humans have gazed up at the sky and made sense of the stars by finding shapes in them — constellations of heroes, animals, and well-worn tales. Now, to celebrate the 10th mission year of NASA’s Fermi Gamma-ray Space Telescope, scientists have used the telescope to develop a new set of constellations that correspond with gamma-ray emissions.

Gamma rays are the most powerful in the electromagnetic spectrum, and they’re typically only produced by very powerful objects. Supermassive black holes at the center of galaxies emit gamma rays, and gamma rays can also spring from explosive gamma-ray bursts, pulsars, the debris of supernova explosions, and more. The Fermi telescope has spent the last decade scanning the sky to compile list of gamma ray sources in the observable universe. That’s given them an array of points, similar to the stars we see shining in the visible spectrum.

In what is known as the “gamma-ray sky,” scientists have devised constellations inspired by many of the same things that inspired the starlight constellations our ancestors gazed at.

The “original” constellations primarily fall into three categories: myths and legends, meaningful topics and common creatures and items, NASA Goddard’s Elizabeth Ferrara, who led the constellation project, explained in a teleconference. The Fermi constellations from the gamma-ray sky are also derived from three categories: modern legends, team partners, and Fermi science. To make sure they didn’t look too much like stars, the team behind these constellations used artificial color to distinguish them.

Familiar Shapes

There are 21 Fermi constellations, including the Hulk (created from a gamma-ray mishap), Godzilla, the Starship Enterprise from “Star Trek: The Next Generation”, the TARDIS from “Doctor Who”, gamma-ray bursts, dark lightning, spider pulsars. Important landmarks from partner nations show up as well: Mt. Fuji for Japan, the Colosseum to represent Italy and more. The constellations even include a Saturn V rocket to represent Huntsville, Alabama where the gamma-ray burst monitor team is centered.

“The hope, of course, is to make the gamma-ray sky more acceptable,” Ferrara said. “By creating constellations that tie into themes that people already know and think about, we hope to bring gamma-ray science into their thoughts.”

Ferrara and Daniel Kocevski, from NASA’s Marshall Space Flight Center, have developed an interactive webpage so that the public can easily engage with these constellations. The interactive site uses a map of the gamma-ray sky from Fermi and artwork from Aurore Simonnet, an illustrator at Sonoma State University in Rohnert Park, California.

Users on the site can explore the gamma-ray sky themselves and learn about the name, artwork, and details behind each constellation.

See the full article here .

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From NASA Fermi: “NASA’s Fermi Traces Source of Cosmic Neutrino to Monster Black Hole”

From NASA Fermi

July 12, 2018

Felicia Chou
Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Dewayne Washington
Goddard Space Flight Center, Greenbelt, Md.
301-286-0040
dewayne.a.washington@nasa.gov

For the first time ever, scientists using NASA’s Fermi Gamma-ray Space Telescope have found the source of a high-energy neutrino from outside our galaxy. This neutrino traveled 3.7 billion years at almost the speed of light before being detected on Earth. This is farther than any other neutrino whose origin scientists can identify.

High-energy neutrinos are hard-to-catch particles that scientists think are created by the most powerful events in the cosmos, such as galaxy mergers and material falling onto supermassive black holes. They travel at speeds just shy of the speed of light and rarely interact with other matter, allowing them to travel unimpeded across distances of billions of light-years.

The neutrino was discovered by an international team of scientists using the National Science Foundation’s IceCube Neutrino Observatory at the Amundsen–Scott South Pole Station.

U Wisconsin ICECUBE neutrino detector at the South Pole

Lunar Icecube

IceCube DeepCore annotated

IceCube PINGU annotated

DM-Ice II at IceCube annotated

Fermi found the source of the neutrino by tracing its path back to a blast of gamma-ray light from a distant supermassive black hole in the constellation Orion.

“Again, Fermi has helped make another giant leap in a growing field we call multimessenger astronomy,” said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington. “Neutrinos and gravitational waves deliver new kinds of information about the most extreme environments in the universe. But to best understand what they’re telling us, we need to connect them to the ‘messenger’ astronomers know best—light.”

Scientists study neutrinos, as well as cosmic rays and gamma rays, to understand what is going on in turbulent cosmic environments such as supernovas, black holes and stars. Neutrinos show the complex processes that occur inside the environment, and cosmic rays show the force and speed of violent activity. But, scientists rely on gamma rays, the most energetic form of light, to brightly flag what cosmic source is producing these neutrinos and cosmic rays.

“The most extreme cosmic explosions produce gravitational waves, and the most extreme cosmic accelerators produce high-energy neutrinos and cosmic rays,” says Regina Caputo of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the analysis coordinator for the Fermi Large Area Telescope Collaboration. “Through Fermi, gamma rays are providing a bridge to each of these new cosmic signals.”

The discovery is the subject of two papers published Thursday in the journal Science.

The source identification paper also includes important follow-up observations by the Major Atmospheric Gamma Imaging Cherenkov Telescopes and additional data from NASA’s Neil Gehrels Swift Observatory and many other facilities.

CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory,Mount Hopkins, Arizona, US in AZ, USA, Altitude 2,606 m (8,550 ft)

NASA Neil Gehrels Swift Observatory

On Sept. 22, 2017, scientists using IceCube detected signs of a neutrino striking the Antarctic ice with energy of about 300 trillion electron volts—more than 45 times the energy achievable in the most powerful particle accelerator on Earth. This high energy strongly suggested that the neutrino had to be from beyond our solar system. Backtracking the path through IceCube indicated where in the sky the neutrino came from, and automated alerts notified astronomers around the globe to search this region for flares or outbursts that could be associated with the event.

Data from Fermi’s Large Area Telescope revealed enhanced gamma-ray emission from a well-known active galaxy at the time the neutrino arrived. This is a type of active galaxy called a blazar, with a supermassive black hole with millions to billions of times the Sun’s mass that blasts jets of particles outward in opposite directions at nearly the speed of light. Blazars are especially bright and active because one of these jets happens to point almost directly toward Earth.

Fermi scientist Yasuyuki Tanaka at Hiroshima University in Japan was the first to associate the neutrino event with the blazar designated TXS 0506+056 (TXS 0506 for short).

“Fermi’s LAT monitors the entire sky in gamma rays and keeps tabs on the activity of some 2,000 blazars, yet TXS 0506 really stood out,” said Sara Buson, a NASA Postdoctoral Fellow at Goddard who performed the data analysis with Anna Franckowiak, a scientist at the Deutsches Elektronen-Synchrotron research center in Zeuthen, Germany. “This blazar is located near the center of the sky position determined by IceCube and, at the time of the neutrino detection, was the most active Fermi had seen it in a decade.”

For more about NASA’s Fermi mission, visit:

https://www.nasa.gov/fermi

See the full article here .

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The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

From NASA Goddard and NASA/Fermi via phys.org: “Multiple gamma-ray emission regions detected in the blazar 3C 279”

From NASA Goddard Space Flight Center

NASA Fermi

phys.org

May 23, 2018
Tomasz Nowakowski

An example composite image of 3C 279 convolved with a beam size of 0.1 mas (circle in the bottom left corner). The contours represent the total intensity while the color scale is for polarized intensity image of 3C 279. The line segments (length of the segments is proportional to fractional polarization) marks the EVPA direction. Credit: Rani et al., 2018.

Using very long baseline interferometry (VLBI), astronomers have investigated the magnetic field topology of the blazar 3C 279, uncovering the presence of multiple gamma-ray emission regions in this source. The discovery was presented May 11 in a paper published in The Astrophysical Journal.

Blazars, classified as members of a larger group of active galaxies that host active galactic nuclei (AGN), are the most numerous extragalactic gamma-ray sources. Their characteristic features are relativistic jets pointed almost exactly toward the Earth. In general, blazars are perceived by astronomers as high-energy engines serving as natural laboratories to study particle acceleration, relativistic plasma processes, magnetic field dynamics and black hole physics.

NASA’s Fermi Gamma-ray Space Telescope is an essential instrument for blazar studies. The spacecraft is equipped with in the Large Area Telescope (LAT), which allows it to detect photons with energy from about 20 million to about 300 billion electronvolts. So far, Fermi has discovered more than 1,600 blazars.

NASA/Fermi LAT

A team of astronomers led by Bindu Rani of NASA’s Goddard Space Flight Center has analyzed the data provided by LAT and by the U.S.-based Very Long Baseline Array (VLBA) to investigate the blazar 3C 279.

NRAO VLBA

The studied object, located in the constellation Virgo. It is one of the brightest and most variable sources in the gamma-ray sky monitored by Fermi. The data allowed Rani’s team to uncover more insight into the nature of gamma-ray emission from this blazar.

“Using high-frequency radio interferometry (VLBI) polarization imaging, we could probe the magnetic field topology of the compact high-energy emission regions in blazars. A case study for the blazar 3C 279 reveals the presence of multiple gamma-ray emission regions,” the researchers wrote in the paper.

Six gamma-ray flares were observed in 3C 279 between November 2013 and August 2014. The researchers also investigated the morphological changes in the blazar’s jet.

The team found that ejection of a new component (designated NC2) during the first three gamma-ray flares suggests the VLBI core as the possible site of the high-energy emission. Furthermore, a delay between the last three flares and the ejection of a new component (NC3) indicates that high-energy emission in this case is located upstream of the 43 GHz core (closer to the blazar’s black hole).

The astronomers concluded that their results are indicative of multiple sites of high-energy dissipation in 3C 279. Moreover, according to the authors of the paper, their study proves that VLBI is the most promising technique to probe the high-energy dissipation regions. However, they added that still more observations are needed to fully understand these features and mechanisms behind them.

“The Fermi mission will continue observing the GeV sky at least for next couple of years. The TeV missions are on their way to probe the most energetic part of the electromagnetic spectrum. High-energy polarization observations (AMEGO, IXPE, etc.) will be of extreme importance in understanding the high-energy dissipation mechanisms,” the researchers concluded.

See the full article here.

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Please help promote STEM in your local schools.

Stem Education Coalition

The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

NASA/Goddard Campus

From ANU: “Mysterious signal comes from very old stars at centre of our galaxy”

Australian National University

March 12, 2018
No writer credit found.

FOR INTERVIEW:
Dr Roland Crocker
Research School of Astronomy and Astrophysics
ANU College of Science
P: +61 2 6125 0253
M: +61 438 499 129
E: Roland.Crocker@anu.edu.au

Will Wright
ANU Media Team
+61 2 6125 7979,
+61 478 337 740
media@anu.edu.au

No image caption or credit.

A team of astronomers involving The Australian National University (ANU) has discovered that a mysterious gamma-ray signal from the centre of the Milky Way comes from 10 billion-year-old stars, rather than dark matter as previously thought.

The Fermi view of the gamma-ray sky. (NASA/DOE/Fermi LAT Collaboration)

NASA/Fermi LAT

NASA/Fermi Gamma Ray Space Telescope

Co-researcher Dr Roland Crocker from ANU said the team had a working hypothesis that the signal was being emitted from thousands of rapidly spinning neutron stars called millisecond pulsars.

“At the distance to the centre of our galaxy, the emission from many thousands of these whirling dense stars could be blending together to imitate the smoothly distributed signal we expect from dark matter,” said Dr Crocker from the ANU Research School of Astronomy and Astrophysics.

“Millisecond pulsars close to the Earth are known to be gamma-ray emitters.”

Dr Crocker said the findings ruled out a provocative theory that dark matter, which is not well understood by scientists, was the origin of the gamma-ray signal.

There is broad scientific consensus that dark matter – matter that scientists cannot see – is widely present in the Universe and helps explain how galaxies hold together rather than fly apart as they spin.

“It is thought that dark matter is composed of Weakly Interacting Massive Particles, which would be expected to gather in the centre of our galaxy,” Dr Crocker said.

“The theory is that, very occasionally, these particles crash into each other and radiate light a billion times more energetic than visible light.”

The Fermi Gamma-Ray Space Telescope, which has been in a low Earth orbit since 2008, has given scientists their clearest ever view of the gamma-ray sky in this energy range.

“While the centre of our galaxy may be rich in dark matter, it is also populated by ancient stars that make up a structure called the Galactic bulge,” Dr Crocker said.

He said the signal detected by Fermi closely traces the distribution of stars in the Galactic bulge.

“Ongoing observational and theoretical work is underway to verify or refute the hypothesis that the gamma-ray signal comes from millisecond pulsars,” Dr Crocker said.

ANU and research institutions in the United States, New Zealand and Germany conducted the study, which was led by Virginia Tech in the US.

The study is published in Nature Astronomy.

See the full article here .

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ANU is a world-leading university in Australia’s capital city, Canberra. Our location points to our unique history, ties to the Australian Government and special standing as a resource for the Australian people.

Our focus on research as an asset, and an approach to education, ensures our graduates are in demand the world-over for their abilities to understand, and apply vision and creativity to addressing complex contemporary challenges.

From UCSC: ” Novel search strategy advances the hunt for primordial black holes”

UC Santa Cruz

February 21, 2018
Tim Stephens
stephens@ucsc.edu

Some theories of the early universe predict density fluctuations that would have created small “primordial black holes,” some of which could be drifting through our galactic neighborhood today and might even be bright sources of gamma rays.

Researchers analyzing data from the Fermi Gamma-ray Space Telescope for evidence of nearby primordial black holes have come up empty, but their negative findings still allow them to put an upper limit on the number of these tiny black holes that might be lurking in the vicinity of Earth.

NASA/Fermi Gamma Ray Space Telescope

NASA’s Fermi Gamma-ray Space Telescope is a powerful space observatory that opens a wide window on the universe. Primordial black holes are a potential source of gamma rays, the highest-energy form of light. (Illustration credit: NASA)

“Understanding how many primordial black holes are around today can help us understand the early universe better,” said Christian Johnson, a graduate student in physics at UC Santa Cruz who developed an algorithm to search data from Fermi’s Large Area Telescope (LAT) for the signatures of primordial black holes. Johnson is a corresponding author of a paper on the findings that has been accepted for publication in The Astrophysical Journal.

Low-mass black holes are expected to emit gamma rays due to Hawking radiation, a theoretical prediction from the work of physicist Stephen Hawking and others. Hawking showed that quantum effects can give rise to particle-antiparticle pairs near the event horizon of a black hole, allowing one of the particles to fall into the black hole and the other to escape. The result is that the black hole emits radiation and loses mass.

A small black hole that isn’t absorbing enough from its environment to offset the losses from Hawking radiation will steadily lose mass and eventually evaporate entirely. The smaller it gets, the brighter it “burns,” emitting more and more Hawking radiation before exploding in a final cataclysm. Previous searches for primordial black holes using ground-based gamma-ray observatories have looked for these brief explosions, but Fermi should be able to detect the “burn phase” occurring over a period of several years.

A limitation of the Fermi search was that it could only extend a relatively short distance from Earth (a small fraction of the distance to the nearest star). The advantage of looking nearby, however, is that primordial black holes could be distinguished from other sources of gamma rays by their movement on the sky.

“It’s like looking at the sky at night and trying to decide if something is an airplane or a star,” Johnson explained. “If it’s an airplane, it will move, and if it’s a star it will stay put.”

Any primordial black holes still around today would have started out much larger and have been gradually losing mass for billions of years. To detect one with Fermi, it would have to have reached the final burn phase during the roughly four-year observation period of the study. Over a period of a few years, it would go from undetectably dim to extremely bright, and would burn brightly for several years before exploding, Johnson said.

“Even though we didn’t detect any, the non-detection sets a limit on the rate of explosions and gives us better constraints than previous research,” he said.

In addition to Johnson, the other corresponding authors of the paper include Steven Ritz, professor of physics and director of the Santa Cruz Institute of Particle Physics at UCSC; and Stefan Funk and Dmitry Malyshev at the Erlangen Centre for Astroparticle Physics in Germany. Other members of the Fermi-LAT Collaboration also contributed to this work and are coauthors of the paper.

See the full article here .

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Shane Telescope at UCO Lick Observatory, UCSC

Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

UCSC is the home base for the Lick Observatory.

Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

Search for extraterrestrial intelligence expands at Lick Observatory
New instrument scans the sky for pulses of infrared light
March 23, 2015
By Hilary Lebow

The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

“Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

“The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

“We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

“This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

“Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

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UCSC is the home base for the Lick Observatory.

From Goddard: “NASA’s SuperTIGER Balloon Flies Again to Study Heavy Cosmic Particles”

NASA Goddard Space Flight Center

Dec. 6, 2017
Francis Reddy
francis.j.reddy@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.

A science team in Antarctica is preparing to loft a balloon-borne instrument to collect information on cosmic rays, high-energy particles from beyond the solar system that enter Earth’s atmosphere every moment of every day. The instrument, called the Super Trans-Iron Galactic Element Recorder (SuperTIGER), is designed to study rare heavy nuclei, which hold clues about where and how cosmic rays attain speeds up to nearly the speed of light.

NASA’s Super-TIGER balloon

The launch is expected by Dec. 10, weather permitting.

Explore this infographic [on the full article] to learn more about SuperTIGER, cosmic rays and scientific ballooning.
Credits: NASA’s Goddard Space Flight Center

Download infographic as PDF

“The previous flight of SuperTIGER lasted 55 days, setting a record for the longest flight of any heavy-lift scientific balloon,” said Robert Binns, the principal investigator at Washington University in St. Louis, which leads the mission. “The time aloft translated into a long exposure, which is important because the particles we’re after make up only a tiny fraction of cosmic rays.”

The most common cosmic ray particles are protons or hydrogen nuclei, making up roughly 90 percent, followed by helium nuclei (8 percent) and electrons (1 percent). The remainder contains the nuclei of other elements, with dwindling numbers of heavy nuclei as their mass rises. With SuperTIGER, researchers are looking for the rarest of the rare — so-called ultra-heavy cosmic ray nuclei beyond iron, from cobalt to barium.

“Heavy elements, like the gold in your jewelry, are produced through special processes in stars, and SuperTIGER aims to help us understand how and where this happens,” said lead co-investigator John Mitchell at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re all stardust, but figuring out where and how this stardust is made helps us better understand our galaxy and our place in it.”

When a cosmic ray strikes the nucleus of a molecule of atmospheric gas, both explode in a shower of subatomic shrapnel that triggers a cascade of particle collisions. Some of these secondary particles reach detectors on the ground, providing information scientists can use to infer the properties of the original cosmic ray. But they also produce an interfering background that is greatly reduced by flying instruments on scientific balloons, which reach altitudes of nearly 130,000 feet (40,000 meters) and float above 99.5 percent of the atmosphere.

The most massive stars forge elements up to iron in their cores and then explode as supernovas, dispersing the material into space. The explosions also create conditions that result in a brief, intense flood of subatomic particles called neutrons. Many of these neutrons can “stick” to iron nuclei. Some of them subsequently decay into protons, producing new elements heavier than iron.

Supernova blast waves provide the boost that turns these particles into high-energy cosmic rays.

NASA’s Fermi Proves Supernova Remnants Produce Cosmic Rays. February 14, 2013.

NASA/Fermi Telescope

NASA/Fermi LAT

As a shock wave expands into space, it entraps and accelerates particles until they reach energies so extreme they can no longer be contained.

On Dec. 1, SuperTIGER was brought onto the deck of Payload Building 2 at McMurdo Station, Antarctica, to test communications in preparation for its second flight. Mount Erebus, the southernmost active volcano on Earth, appears in the background.
Credits: NASA/Jason Link

Over the past two decades, evidence accumulated from detectors on NASA’s Advanced Composition Explorer satellite and SuperTIGER’s predecessor, the balloon-borne TIGER instrument, has allowed scientists to work out a general picture of cosmic ray sources. Roughly 20 percent of cosmic rays were thought to arise from massive stars and supernova debris, while 80 percent came from interstellar dust and gas with chemical quantities similar to what’s found in the solar system.

“Within the last few years, it has become apparent that some or all of the very neutron-rich elements heavier than iron may be produced by neutron star mergers instead of supernovas,” said co-investigator Jason Link at Goddard.

Neutron stars are the densest objects scientists can study directly, the crushed cores of massive stars that exploded as supernovas. Neutron stars orbiting each other in binary systems emit gravitational waves, which are ripples in space-time predicted by Einstein’s general theory of relativity. These waves remove orbital energy, causing the stars to draw ever closer until they eventually crash together and merge.

Theorists calculated that these events would be so thick with neutrons they could be responsible for most of the very neutron-rich cosmic rays heavier than nickel. On Aug. 17, NASA’s Fermi Gamma-ray Space Telescope and the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory detected the first light and gravitational waves from crashing neutron stars. Later observations by the Hubble and Spitzer space telescopes indicate that large amounts of heavy elements were formed in the event.

“It’s possible neutron star mergers are the dominant source of heavy, neutron-rich cosmic rays, but different theoretical models produce different quantities of elements and their isotopes,” Binns said. “The only way to choose between them is to measure what’s really out there, and that’s what we’ll be doing with SuperTIGER.”

SuperTIGER is funded by the NASA Headquarters Science Mission Directorate Astrophysics Division.

The National Science Foundation (NSF) Office of Polar Programs manages the U.S. Antarctic Program and provides logistic support for all U.S. scientific operations in Antarctica. NSF’s Antarctic support contractor supports the launch and recovery operations for NASA’s Balloon Program in Antarctica. Mission data were downloaded using NASA’s Tracking and Data Relay Satellite System.

For more information about NASA’s Balloon Program, visit:

http://www.nasa.gov/balloons

See the full article here.

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NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

NASA/Goddard Campus

From astrobites: “Future Gamma-ray Telescopes and the Search for Dark Matter”

Astrobites

Oct 3, 2017
Nora Shipp

Title: Resolving Dark Matter Subhalos With Future Sub-GeV Gamma-Ray Telescopes
Authors: Ti-Lin Chou, Dimitrios Tanoglidis, and Dan Hooper
First Author’s Institution: Dept. of Physics, University of Chicago, USA

Status: Submitted to the Journal of Cosmology and Astroparticle Physics (open access)

We are surrounded by undetected dark matter.

Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

In fact, our entire Galaxy is enveloped in a large halo of it, but because dark matter does not emit or reflect light, the halo is completely invisible.

Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

Milky Way NASA/JPL-Caltech /ESO R. Hurt

Inside this halo, orbiting our galaxy, are hundreds of smaller, equally invisible dark matter halos (Figure 1).

Figure 1. Galaxies like the Milky Way are surrounded by small dark matter halos (blue blobs). Some of these halos contain no stars, but could still produce gamma-rays from dark matter annihilation! Source: ESO

The larger ones contain their own dwarf galaxies, but the smallest halos are so tiny that they contain no stars at all. However, if the leading theory of WIMP (Weakly Interacting Massive Particle) dark matter is correct, there is one way that we could actually see these dark matter halos without the help of any stars. If dark matter particles are their own antiparticle, they would annihilate when they come into contact with each other, producing various particles, including highly energetic photons known as gamma-rays.

Gamma-rays have millions of times more energy than the optical photons that human eyes can see, yet these energetic particles are quite difficult to detect. The current leader in gamma-ray detection is the Fermi Gamma-ray Space Telescope, a satellite that has been orbiting the Earth, searching the sky for gamma-rays, for almost 10 years.

NASA/Fermi Telescope

NASA/Fermi LAT

Since Fermi was first launched, scientists have searched the gamma-ray sky for evidence of dark matter annihilation. What makes this search really tricky is that dark matter is not the only thing that produces gamma-rays. The sky is actually full of gamma-rays coming from all directions, produced by clouds of gas, pulsars, and active galactic nuclei, among many other sources (Figure 2 [not shown in article, replaced here).

Fermi’s Latest Gamma-ray Census Highlights Cosmic Mysteries

However, those tiny dark matter halos that don’t contain stars or gas or any kind of non-dark matter should only be producing gamma-rays from dark matter annihilation. The catch is that we have no idea where these dark matter halos are. Scientists, therefore, have searched all across the sky for gamma-rays that might be coming from dark halos, and they just might have found a couple.

Two sources of gamma-rays fit all the requirements – they are in the right part of the sky, do not emit any other kind of light (as you’d expect from a halo containing only dark matter), and appear to extend wider across the sky than the single point of a far away star. However, it’s impossible to tell whether these sources are really extended like a dark matter halo or whether they are just two star-like points so close to each other that they blur together, appearing to Fermi as a single blob. Today’s paper considers whether a proposed successor to Fermi called e-ASTROGAM (Figure 3) will be able to resolve the mystery of these gamma-ray blobs.

Figure 3. A model of e-Astrogam, one potential successor to the Fermi Gamma-ray Space Telescope. Source: ESA

Are they in fact dark matter halos (in which case this would be the first confirmed detection of dark matter annihilation!) or are they simply two points blurred into one?

e-ASTROGAM would be quite similar to Fermi, but with several important changes. The biggest difference is that it would be able to detect gamma-rays at a slightly lower energy than Fermi, giving us a brand new view of the gamma-ray sky. In the context of today’s paper, however, the most significant difference is the angular resolution. Angular resolution determines how close together two objects can get before they blur together into a single blob. The angular resolution of e-ASTROGAM will be about 4-6 times better than Fermi’s in the energy range of these mysterious gamma-ray sources. According to the authors of today’s paper, this should definitely be enough to tell whether they are single extended objects or two independent points that are just too close together for Fermi to see (Figure 4).

Figure 4. Simulated images of two point sources as seen by Fermi and e-ASTROGAM. On the left, Fermi is unable to distinguish between the two objects, seeing only a single blob of gamma-rays. On the right, e-ASTROGAM, with its superior angular resolution, can tell that the single blob is actually two individual objects. Source: Figure 3 of the paper.

In order to see just how well e-ASTROGAM will be able to see these objects, the authors modeled fake observations of dark matter annihilation from an extended halo and from two point sources. They determined for different halo sizes and dark matter particles how well e-ASTROGAM will be able to tell whether an object is one extended source or two points. Figure 5 illustrates the difference e-ASTROGAM will make in confirming the nature of these gamma-ray sources. The green and red lines represent how easily Fermi and e-ASTROGAM can distinguish pairs of sources (x-axis) as a function of source brightness (y-axis). e-ASTROGAM reaches much farther along the x-axis, indicating that it can much more easily resolve two point sources. The precise numbers change for different dark matter halos and particles, but in all cases e-ASTROGAM shows a significant improvement over Fermi.

Figure 5. This plot illustrates how e-ASTROGAM will be able to help distinguish between extended dark matter halos and two nearby points. The y-axis shows how bright the object in question is, and the x-axis is related to how easily the telescope can distinguish between two nearby points and a single extended object. Even with really bright objects Fermi (green) has a hard time distinguishing between the two scenarios, while e-ASTROGAM (red) can more easily tell the difference. Source: Figure 5 of the paper.

A future gamma-ray telescope like e-ASTROGAM will be an essential tool in determining whether Fermi has in fact detected dark matter annihilation from dark halos. In addition to determining whether the two potential halos detected by Fermi are actually just pairs of close-together point sources, e-ASTROGAM may be able to detect gamma-rays from even more dark matter halos that are too faint for Fermi to observe on its own. e-ASTROGAM with its superior angular resolution and lower energy range would provide a brand new view of the gamma-ray universe, giving us unexpected insight into known and unknown sources of gamma-rays, and perhaps finally revealing the nature of dark matter.

See the full article here .

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What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

From Symmetry: “The rise of LIGO’s space-studying super-team”

Symmetry

06/27/17
Troy Rummler

The era of multi-messenger astronomy promises rich rewards—and a steep learning curve.

NASA/Fermi LAT

Sometimes you need more than one perspective to get the full story.

Scientists including astronomers working with the Fermi Large Area Telescope have recorded brief bursts of high-energy photons called gamma rays coming from distant reaches of space. They suspect such eruptions result from the merging of two neutron stars—the collapsed cores of dying stars—or from the collision of a neutron star and a black hole.

But gamma rays alone can’t tell them that. The story of the dense, crashing cores would be more convincing if astronomers saw a second signal coming from the same event—for example, the release of ripples in space-time called gravitational waves.

Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

“The Fermi Large Area Telescope detects a few short gamma ray bursts per year already, but detecting one in correspondence to a gravitational-wave event would be the first direct confirmation of this scenario,” says postdoctoral researcher Giacomo Vianello of the Kavli Institute for Particle Astrophysics and Cosmology, a joint institution of SLAC National Accelerator Laboratory and Stanford University.

Scientists discovered gravitational waves in 2015 (announced in 2016). Using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, they detected the coalescence of two massive black holes.

Caltech/MIT Advanced aLigo Hanford, WA, USA installation

Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

ESA/eLISA the future of gravitational wave research

LIGO scientists are now sharing their data with a network of fellow space watchers to see if any of their signals match up. Combining multiple signals to create a more complete picture of astronomical events is called multi-messenger astronomy.​

Looking for a match

“We had this dream of finding astronomical events to match up with our gravitational wave triggers,” says LIGO scientist Peter Shawhan of the University of Maryland. ​

But LIGO can only narrow down the source of its signals to a region large enough to contain roughly 100,000 galaxies.

Searching for contemporaneous signals within that gigantic volume of space is extremely challenging, especially since most telescopes only view a small part of the sky at a time. So Shawhan and his colleagues developed a plan to send out an automatic alert to other observatories whenever LIGO detected an interesting signal of its own. The alert would contain preliminary calculations and the estimated location of the source of the potential gravitational waves.

“Our early efforts were pretty crude and only involved a small number of partners with telescopes, but it kind of got this idea started,” Shawhan says. The LIGO Collaboration and the Virgo Collaboration, its European partner, revamped and expanded the program while upgrading their detectors. Since 2014, 92 groups have signed up to receive alerts from LIGO, and the number is growing.

LIGO is not alone in latching onto the promise of multi-messenger astronomy. The Supernova Early Warning System (SNEWS) also unites multiple experiments to look at the same event in different ways.

Neutral, rarely interacting particles called neutrinos escape more quickly from collapsing stars than optical light, so a network of neutrino experiments is prepared to alert optical observatories as soon as they get the first warning of a nearby supernova in the form of a burst of neutrinos.

National Science Foundation Director France Córdova has lauded multi-messenger astronomy, calling it in 2016 a bold research idea that would lead to transformative discoveries.​

The learning curve

Catching gamma ray bursts alongside gravitational waves is no simple feat.

The Fermi Large Area Telescope orbits the earth as the primary instrument on the Fermi Gamma-ray Space Telescope.

NASA/Fermi Telescope

The telescope is constantly in motion and has a large field of view that surveys the entire sky multiple times per day.

But a gamma-ray burst lasts just a few seconds, and it takes about three hours for LAT to complete its sweep. So even if an event that releases gravitational waves also produces a gamma-ray burst, LAT might not be looking in the right direction at the right time. It would need to catch the afterglow of the event.

Fermi LAT scientist Nicola Omodei of Stanford University acknowledges another challenge: The window to see the burst alongside gravitational waves might not line up with the theoretical predictions. It’s never been done before, so the signal could look different or come at a different time than expected.

That doesn’t stop him and his colleagues from trying, though. “We want to cover all bases, and we adopt different strategies,” he says. “To make sure we are not missing any preceding or delayed signal, we also look on much longer time scales, analyzing the days before and after the trigger.”

Scientists using the second instrument on the Fermi Gamma-ray Space Telescope have already found an unconfirmed signal that aligned with the first gravitational waves LIGO detected, says scientist Valerie Connaughton of the Universities Space Research Association, who works on the Gamma-Ray Burst Monitor. “We were surprised to find a transient event 0.4 seconds after the first GW seen by LIGO.”

While the event is theoretically unlikely to be connected to the gravitational wave, she says the timing and location “are enough for us to be interested and to challenge the theorists to explain how something that was not expected to produce gamma rays might have done so.”

From the ground up

It’s not just space-based experiments looking for signals that align with LIGO alerts. A working group called DESgw, members of the Dark Energy Survey with independent collaborators, have found a way to use the Dark Energy Camera, a 570-Megapixel digital camera mounted on a telescope in the Chilean Andes, to follow up on gravitational wave detections.​

Dark Energy Camera [DECam], built at FNAL

NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

“We have developed a rapid response system to interrupt the planned observations when a trigger occurs,” says DES scientist Marcelle Soares-Santos of Fermi National Accelerator Laboratory. “The DES is a cosmological survey; following up gravitational wave sources was not originally part of the DES scientific program.”

Once they receive a signal, the DESgw collaborators meet to evaluate the alert and weigh the cost of changing the planned telescope observations against what scientific data they could expect to see—most often how much of the LIGO source location could be covered by DECam observations.

“We could, in principle, put the telescope onto the sky for every event as soon as night falls,” says DES scientist Jim Annis, also of Fermilab. “In practice, our telescope is large and the demand for its time is high, so we wait for the right events in the right part of the sky before we open up and start imaging.”

At an even lower elevation, scientists at the IceCube neutrino experiment—made up of detectors drilled down into Antarctic ice—are following LIGO’s exploits as well.

U Wisconsin ICECUBE neutrino detector at the South Pole

Lunar Icecube

IceCube DeepCore

IceCube PINGU

DM-Ice II at IceCube

“The neutrinos IceCube is looking for originate from the most extreme environment in the cosmos,” says IceCube scientist Imre Bartos of Columbia University. “We don’t know what these environments are for sure, but we strongly suspect that they are related to black holes.”

LIGO and IceCube are natural partners. Both gravitational waves and neutrinos travel for the most part unimpeded through space. Thus, they carry pure information about where they originate, and the two signals can be monitored together nearly in real time to help refine the calculated location of the source.

The ability to do this is new, Bartos says. Neither gravitational waves nor high-energy neutrinos had been detected from the cosmos when he started working on IceCube in 2008. “During the past few years, both of them were discovered, putting the field on a whole new footing.”

Shawhan and the LIGO collaboration are similarly optimistic about the future of their program and multi-messenger astronomy. More gravitational wave detectors are planned or under construction, including an upgrade to the European detector Virgo, the KAGRA detector in Japan, and a third LIGO detector in India, and that means scientists will home in closer and closer on their targets.​

VIRGO Gravitational Wave interferometer, near Pisa, Italy

KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

IndIGO LIGO in India

IndIGO in India

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Symmetry is a joint Fermilab/SLAC publication.

From AAS NOVA: “The Discovery of Five Early Gamma-Ray Blazars”

American Astronomical Society

8 March 2017
Susanna Kohler

An artist’s impression of a quasar, in which accretion onto a supermassive black hole powers a high-speed jet. A new study has discovered five such galactic nuclei from the early universe that are pointed toward us. [NASA/Dana Berry (SkyWorks Digital)]

Due to a recent software improvement, the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has discovered five gamma-ray blazars at high redshifts, opening a window to the early universe.

NASA/Fermi LAT

NASA Fermi Telescope

Spotting Pointed Activity

Quasars, the active centers of some distant galaxies, shine brightly across the electromagnetic spectrum. These luminous objects are fueled by material accreting onto a supermassive black hole, and the release of energy in this accretion launches powerful jets that, in the case of a type of quasar called a “blazar”, point along our line of sight — causing them to be relativistically boosted to look especially bright. The jet radiation dominates blazar broadband emission, especially at gamma-ray wavelengths.

Fermi-LAT has detected thousands of blazars in gamma rays; in fact, blazars have been found to be the most numerous gamma-ray population in our sky. In spite of this, Fermi hasn’t found any gamma-ray blazars at a redshift greater than z = 3.1 — likely because at this distance, the blazars’ gamma-ray emission is redshifted to lower frequencies at which the LAT is less sensitive.

A recent, spectacular set of improvements to Fermi data analysis, however, known as Pass 8, has substantially enhanced the sensitivity of LAT to gamma rays across the spectrum — with particular improvement at lower frequencies. Motivated by this increased sensitivity, a team of Fermi scientists has used the data from Pass 8 to search for especially distant gamma-ray-bright blazars.

Maps of the five high-redshift blazars detected by Fermi-LAT. [Ackermann et al. 2017]

Window to the Early Universe

The Fermi team began by selecting high-redshift radio-loud blazars from a known catalog of over a million quasars. They then searched for these ~1100 sources within the 92 months of LAT data produced by Pass 8.

This systematic search led to the detection of five new gamma-ray sources consistent with the positions of blazars at redshifts greater than z = 3.1 — including NVSS J151002+570243, which now qualifies as the most distant gamma-ray blazar known, at a redshift of z = 4.31.

Analysis of the sources’ spectral energy distributions verifies that they have all the properties expected of especially powerful blazars, confirming their identity. Modeling of their spectra suggests they harbor massive black holes in the range of hundreds of millions to tens of billions of solar masses. The properties of these sources allow the authors to estimate the space density of massive black holes hosted in jetted systems: roughly 70 per cubic gigaparsec.

Though these five new gamma-ray blazars may constitute a small sample, they provide information that can be used to begin to constrain our models of how supermassive black holes formed in the early universe. They’re also a shining example of the remarkable benefit possible with clever software improvements!

Citation

M. Ackermann et al 2017 ApJL 837 L5. doi:10.3847/2041-8213/aa5fff

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