From AAS NOVA: ” Two Explosions with Similar Quirks”

From AAS NOVA

12 October 2018
Susanna Kohler

Artist’s by now iconic illustration of the merger of two neutron stars, producing a short gamma-ray burst. [NSF/LIGO/Sonoma State University/A. Simonnet]

High-energy radiation released during the merger of two neutron stars last year has left astronomers puzzled. Could a burst of gamma rays from 2015 help us to piece together a coherent picture of both explosions?

A Burst Alone?

When two neutron stars collided last August, forming a distinctive gravitational-wave signal and a burst of radiation detected by telescopes around the world, scientists knew that these observations would change our understanding of short gamma-ray bursts (GRBs).Though we’d previously observed thousands of GRBs, GRB 170817A was the first to have such a broad range of complementary observations — both in gravitational waves and across the electromagnetic spectrum — providing insight into its origin.

Total isotropic-equivalent energies for Fermi-detected gamma-ray bursts with known redshifts. GRB 170817A (pink star) is a factor of ~1,000 dimmer than typical short GRBs (orange points). GRB 170817A and GRB 150101B (green star) are two of the closest detected short GRBs. [Adapted from Burns et al. 2018]

But it quickly became evident that GRB 170817A was not your typical GRB. For starters, this burst was unusually weak, appearing 1,000 times less luminous than a typical short GRB. Additionally, the behavior of this burst was unusual: instead of having only a single component, the ~2-second explosion exhibited two distinct components — first a short, hard (higher-energy) spike, and then a longer, soft (lower-energy) tail.

The peculiarities of GRB 170817A prompted a slew of models explaining its unusual appearance. Ultimately, the question is: can our interpretations of GRB 170817A safely be applied to the general population of gamma-ray bursts? Or must we assume that GRB 170817A is a unique event, not representative of the general population?

New analysis of a GRB from 2015 — presented in a recent study led by Eric Burns (NASA Goddard SFC) — may help to answer this question.

A Matter of Angles

What does a burst from 2015 have to do with the curious case of GRB 170817A? Burns and collaborators have demonstrated that this 2015 burst, GRB 150101B, exhibited the same strange behavior as GRB 170817A: its emission can be broken down into two components consisting of a short, hard spike, followed by a long, soft tail. Unlike GRB 170817A, however, GRB 150101B is not underluminous — and it lasted less than a tenth of the time.

Fermi count rates in different energy ranges showing the short hard spike and the longer soft tail in GRB 150101B. The short hard spike is visible above 50 keV (top and middle panels). The soft tail is visible in the 10–50 keV channel (bottom panel). [Burns et al. 2018]

Intriguingly, these similarities and differences can all be explained by a single model. Burns and collaborators propose that GRB 150101B and GRB 170817A exhibit the exact same two-component behavior, and their differences in luminosity and duration can be explained by quirks of special relativity.

High-speed outflows such as these will have different apparent luminosities and durations depending on whether we view them along their axis or slightly from the side. Burns and collaborators demonstrate that these the two bursts could easily have the same profile — but GRB 150101B was viewed nearly on-axis, whereas GRB 170817A was viewed from an angle.

If this is true, then perhaps more GRBs have hard spikes and soft tails similar to these two; the tails may just be difficult to detect in more distant bursts. While more work remains to be done, the recognition that GRB 170817A may not be unique is an important one for understanding both its behavior and that of other short GRBs.

Citation

“Fermi GBM Observations of GRB 150101B: A Second Nearby Event with a Short Hard Spike and a Soft Tail,” E. Burns et al 2018 ApJL 863 L34.
http://iopscience.iop.org/article/10.3847/2041-8213/aad813/meta

VIRGO Gravitational Wave interferometer, near Pisa, Italy

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

ESA/eLISA the future of gravitational wave research

Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

NASA/Fermi LAT

NASA/Fermi Gamma Ray Space Telescope

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

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From AAS NOVA: “Oscillations in the Eye of the Bull”

From AAS NOVA

5 October 2018
Kerry Hensley

This illustration shows sound waves propagating through a star’s interior. These acoustic oscillations can be detected in radial velocity measurements of the star. [Gabriel Perez Diaz/Instituto de Astrofisica de Canarias]

Roque de los Muchachos Observatory (Garafía, La Palma). Credit IAC.

Aldebaran, the brightest star in the constellation Taurus, was one of the first stars suspected to harbor an exoplanet. The presence of its planetary companion, Aldebaran b, was confirmed in 2015, and the decades of data preceding the discovery might harbor a few more surprises.

A Recognizable Target

A model of acoustic oscillations, also called p-modes, which can be used to infer fundamental properties of stars through asteroseismology. The vertical extent of the oscillation has been exaggerated by a factor of 1,000. [NASA/MSFC]

Like hundreds of other exoplanets, Aldebaran b was discovered via the radial velocity method, in which the tug of a planet causes a detectable shift in the wavelengths of absorption lines in its parent star’s spectrum.

Radial velocity Image via SuperWasp http:// http://www.superwasp.org/exoplanets.htm

Radial Velocity Method-Las Cumbres Observatory

Radial velocity measurements can reveal more than just the presence of planetary companions, however; periodic oscillations of the star itself can be hidden in the radial velocity signal. These oscillations depend on the fundamental parameters of the star: mass, radius, surface gravity, and effective temperature.

To search for stellar oscillations of Aldebaran, a team of astronomers led by Will Farr (University of Birmingham, UK) delved into more than three decades of historical radial velocity measurements.

Radial velocity measurements from the Hertzsprung SONG Telescope. The long-period planetary signal is superimposed upon the shorter-period p-mode signal. [Farr et al. 2018]

Digging Through the Data

The authors fit to the data a Keplerian model — to confirm the previously discovered planetary signal — and a Continuous Auto-Regressive Moving Average (CARMA) model — to search for stellar oscillations. In addition to verifying the presence of Aldebaran b, Farr and collaborators found evidence for stellar oscillations with maximum power at a frequency of 2.2 microhertz — well within the typical range for a red giant.

The authors followed up on these findings with high-cadence radial velocity observations from the Hertzsprung SONG Telescope and photometry from K2, the revived version of the Kepler Space Telescope. Analysis of both these datasets showed evidence of stellar oscillations consistent with those seen in the more irregularly sampled historical data.

Hertzsprung SONG Telescope at Observatorio del Teide on Mount Teide at 2,390 metres (7,840 ft), located on Tenerife, Spain

A model of the stellar irradiance received at Aldebaran b’s orbital distance over the course of Aldebaran’s main-sequence lifetime. [Farr et al. 2018]

Getting to Know Aldebaran

Farr and collaborators were able to estimate the orbital parameters of Aldebaran b and the mass and age of its parent star. The authors find that Aldebaran has a mass of 1.16 solar masses and an age of 6.4 billion years. This suggests that while Aldebaran is currently more than 500 times more luminous than the Sun, it likely matched the Sun’s output early in its life.

At an orbital distance of 1.5 AU, Aldebaran b probably enjoyed stellar irradiance similar to modern-day Earth in the distant past — about 4.4 billion years ago. However, Aldebaran b is at least 5.8 Jupiter masses (and may be massive enough to be a brown dwarf, depending on the inclination of its orbit), so it’s unlikely to have ever hosted life as we know it.

As Farr and collaborators have shown, it’s possible to extract accurate stellar and orbital parameters from irregularly sampled radial velocity data — which is plentiful thanks to radial-velocity surveys searching for exoplanets. With this technique, we may soon know of thousands of planets around red giant stars!

Citation

“Aldebaran b’s Temperate Past Uncovered in Planet Search Data,” Will M. Farr et al 2018 ApJL 865 L20. http://iopscience.iop.org/article/10.3847/2041-8213/aadfde/meta

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Investigating Our Expanding Universe”

From AAS NOVA

3 October 2018
Susanna Kohler

Could natural inhomogeneity in our universe lead to different local and global measurements of how fast it’s expanding? [Adapted from Macpherson et al. 2018]

The universe is expanding — but we’re still not sure how quickly! With past measurements of this expansion rate causing yielding conflict and debate, a new study investigates whether we can resolve the evident tension.

Conflicting Measurements

Estimated values of the Hubble constant, 2001–2018. Data marked with circles show local, distance-ladder-calibrated measurements; data marked with squares indicate global measurements from the CMB and baryon-acoustic oscillations. [Kintpuash]

The first sign that the universe around us is expanding was found in the late 1920s, when astronomers first recorded evidence that distant galaxies appear to be moving away from us at ever faster rates, the more distant they are. This led to the development of the Hubble constant (H0), a value used to quantify this observed rate of expansion — and its value has been debated ever since.

Though we’ve come a long way since our initial, imprecise measurements of H0, today the two primary methods of measuring the Hubble constant remain in tension:

Local measurements can be made by determining the distances and recession speeds of visible objects in the universe; Type Ia supernova surveys provide the standard candles needed for these measurements. Using this approach, scientists obtain an H0 value around us of ~74 (km/s)/Mpc.
Global measurements are made by estimating the Hubble constant from measurements of the cosmic microwave background (CMB), relic radiation from the Big Bang. By fitting a multi-parameter model to Planck-mission observations of the CMB, scientists obtain a slower expansion estimate of ~68 (km/s)/Mpc for H0.

Inhomogeneity to the Rescue?

This discrepancy of nearly 9% between the two measurements — which cannot be brought into agreement by the measurements’ error bars — remains puzzling. Is one or the other group of astronomers making a mistake, or underestimating their errors? Could there be new physics at play in the cosmological model used to interpret the CMB results?

Expansion rate (left) and density (right) of a simulated inhomogeneous anisotropic universe. [Macpherson et al. 2018]

Some scientists have proposed an alternative explanation: what if the global expansion rate of the universe is not the same as the local rate? One possibility is that we live in a local void, an underdense region of the universe that expands faster than does the universe overall.

To determine whether the tension between the two types of H0 measurements can be explained by such an inhomogeneous universe, a team of scientists led by Hayley Macpherson (Monash University) has explored the behavior of a simulated universe.

A Simulated Universe

The global measurement (Planck measurement; blue solid line) and local measurement (Riess et al. measurement; red solid line) of the Hubble constant can’t be brought into agreement by local deviations in the Hubble constant due to inhomogeneities (blue data showing distribution of various local spheres). [Macpherson et al. 2018]

Macpherson and collaborators simulated the growth of large-scale cosmological structures using numerical relativity. Starting with an inhomogeneous universe, the authors evolved random density fluctuations of the universe from its birth to today, and then investigated what effect these inhomogeneities have on local measurements of the Hubble constant.

The authors find that, in their simulated universe, local measurements of the Hubble constant differ by less than 1% compared to the global value. An inhomogeneous universe therefore cannot explain the nearly 9% difference we measure between the CMB-inferred global and supernova-measured local values of the Hubble constant.

What’s next? It’s back to the drawing board — the mystery of our expanding universe continues to elude us. Here’s hoping that high-precision measurements from future surveys will help us to further refine our understanding!

Citation

“The Trouble with Hubble: Local versus Global Expansion Rates in Inhomogeneous Cosmological Simulations with Numerical Relativity,” Hayley J. Macpherson et al 2018 ApJL 865 L4.
http://iopscience.iop.org/article/10.3847/2041-8213/aadf8c/meta

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Featured Image: A CHIME Search for Fast Radio Bursts”

From AAS NOVA

The Canadian Hydrogen Intensity Mapping Experiment, or CHIME, is a novel radio telescope originally intended to map features in hydrogen gas to measure dark energy. It has an additional mission now, however: CHIME will search the sky for signs of new fast radio bursts (FRBs). FRBs — energetic transient radio pulses that last only a few milliseconds — were first discovered about a decade ago, and though we’ve only observed ~30 of them so far, some estimates suggest they occur at a rate of several hundred to a few thousand per day across the sky! CHIME’s large field of view, high sensitivity, and wide bandwidth will help us hunt for these explosive events. In a new report by the CHIME/FRB collaboration, the team details this unique telescope, located in British Columbia. CHIME is made up of four 20-m x 100-m semicylindrical paraboloid reflectors, giving it its unusual appearance. The team expects that when CHIME begins science operations, it will detect FRBs at a rate of 2–42 FRBs per sky per day. For more information, check out the article below!

Citation

“The CHIME Fast Radio Burst Project: System Overview,” The CHIME/FRB Collaboration et al 2018 ApJ 863 48. http://iopscience.iop.org/article/10.3847/1538-4357/aad188/meta

Related journal articles
_________________________________________________
See the full article for further references with links.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Unexpected Discovery of a Bright Cow”

From AAS NOVA

28 September 2018
Susanna Kohler

Image from the Sloan Digital Sky Survey with cross hairs pinpointing the location of AT2018cow. It is spatially coincident with the galaxy CGCG 137-068 in the constellation Hercules. [Sloan Digital Sky Survey]

SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

The recent discovery of an unusual transient event, nicknamed “the Cow”, has set the community of transient astronomers abuzz (amoo?). What do we know about this odd event so far?

The location of AT2018cow: a post-discovery image (top left), a pre-discovery reference image (top right), a subtracted difference image (bottom left), and a Pan-STARRS multi-color image (bottom right). [Prentice et al. 2018]

Pann-STARSR1 Telescope, U Hawaii, Mauna Kea, Hawaii, USA, Altitude 3,052 m (10,013 ft)

Thinking Outside the Box

Once upon a time, supernovae seemed somewhat well characterized. But with the advent of today’s large, wide-field transient surveys that scan the visible sky every few nights, it seems like we’re now constantly discovering new supernova-like events that don’t quite fit into previous, neatly defined categories.

Among the large variety of new classes of transients uncovered by these surveys are supernova-like events whose lightcurves rise and fall much faster than standard supernovae. One example is AT2017gfo, the first confirmed kilonova, which was paired with the neutron-star merger first detected in gravitational waves in August 2017. Additional examples of these rapidly evolving transients span a wide range of peak absolute magnitudes (from –15 to –22 magnitude) and rise times (~1–10 days), making them difficult to explain through a single scenario.

ATLAS, LT, GROND, and SWIFT light curves of AT2018cow. [Adapted from Prentice et al. 2018]

Now astronomers have found one more unusual, luminous, and fast-evolving transient: AT2018cow. In a new study, a team of astronomers led by Simon Prentice (Queen’s University Belfast, UK) has presented the discovery and initial analysis of the first 18 days of this event.

An Unusual Transient

The Cow was first discovered with ATLAS, a twin 0.5-m telescope system located in Hawaii, on the night of 16 June 2018. Post-discovery monitoring of the Cow with various telescopes spanning optical, near-infrared, and ultraviolet wavelengths reveals a variety of odd properties.

ATLAS is an asteroid impact early warning system of two telescopes being developed by the University of Hawaii and funded by NASA

ATLAS telescope, First Asteroid Terrestrial-impact Last Alert system (ATLAS) fully operational 8/15/15 Haleakala , Hawaii, USA, Altitude 4,205 m (13,796 ft)

2-metre Liverpool Telescope at La Palma in the Canary Islands, Altitude 2,363 m (7,753 ft)

Liverpool Telescope at the Observatorio del Roque de los Muchachos

The Cow’s peak luminosity was remarkably high: ~1.77 x 10^44 erg/s, or about 10–100 times brighter than a typical supernova. It reached the peak very quickly, brightening by more than 5 mag in just 3.3 days, while typical supernovae have rise times of perhaps 10–20 days. In addition, the Cow had a high peak blackbody temperature (~27,000 K), low estimated ejecta mass (just 0.1–0.4 solar masses), and relatively featureless and non-evolving spectra.

ESO GROND imager on 2.2 meter MPG/ESO telescope at LaSilla

ESO GROND imager on 2.2 meter MPG/ESO telescope at LaSilla

ESO 2.2 meter telescope 600 km north of Santiago de Chile at Cerro LaSilla, at an altitude of 2400 metres

NASA Neil Gehrels Swift Observatory

Magnetar from a Collision?

The combination of the Cow’s odd properties eliminates a number of more common progenitor explanations, such as supernova shock breakout. The authors do explore one scenario that could produce properties similar to the Cow’s, however: the formation of a magnetar — a strongly magnetized neutron star — from the merger of a binary neutron star system. Such a model, Prentice and collaborators say, would predict a transient with a peak luminosity, decline rate, and effective temperature that are all consistent with those of the Cow.

How can we confirm this picture? The next step will be to compare additional observations of AT2018cow in radio and X-ray wavelengths — which were made simultaneously with those reported here in near-infared through ultraviolet — to the magnetar models to see if the models also match those observations. If so, we may have an explanation for this unusual transient.

Citation

“The Cow: Discovery of a Luminous, Hot, and Rapidly Evolving Transient,” S. J. Prentice et al 2018 ApJL 865 L3. http://iopscience.iop.org/article/10.3847/2041-8213/aadd90/meta

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Planning for Images of a Black Hole”

From AAS NOVA

24 September 2018
Susanna Kohler

Some example snapshots of the simulated shadow of the event horizon of a black hole. The images from this simulation demonstrate what we expect to see in 1.3-mm emission in eventual images from the Event Horizon Telescope. [Adapted from Medeiros et al. 2018]

In 2006 an ambitious project was begun: creating the world’s largest telescope with the goal of imaging the shadow of a black hole. But how will we analyze the images this project produces?

A Planet-Sized Telescope

Event Horizon Telescope Array

The locations of the participating telescopes of the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) as of March 2017. Jointly, these telescopes plan to image the shadow of the event horizon of the supermassive black hole at the center of the Milky Way. [ESO/O. Furtak]

Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

Atacama Pathfinder EXperiment

Combined Array for Research in Millimeter-wave Astronomy (CARMA)

Atacama Submillimeter Telescope Experiment (ASTE)

Caltech Submillimeter Observatory (CSO)

Institut de Radioastronomie Millimetrique (IRAM) 30m

James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

Large Millimeter Telescope Alfonso Serrano

Submillimeter Array Hawaii SAO

ESO/NRAO/NAOJ ALMA Array, Chile

South Pole Telescope SPTPOL

NSF CfA Greenland telescope

Greenland Telescope

Future Array/Telescopes

Plateau de Bure interferometer

The Event Horizon Telescope (EHT) is composed of radio observatories around the world. These observatories combine their data using very-long-baseline interferometry to create a virtual telescope that has an effective diameter of the entire planet!

The EHT, researchers hope, will have the power to peer in millimeter emission down to the very horizon of an accreting black hole — specifically, Sgr A*, the supermassive black hole in the Milky Way’s center — to learn about black-hole physics and general relativity in the depths of this monster’s gravitational pull.

Today, the EHT is closer than ever to its goal, as the project continues to increase its resolving power and sensitivity as more telescopes join the system. Another important aspect of this project exists, however: the ability to analyze and characterize the images it produces in a meaningful way.

A simple example of using principal component analysis to decompose a set of images into independent eigenimages. The example images (top row) are snapshots from a simple model of a Gaussian spot moving on a circular path. The first four components of the principal component analysis decomposition — the four leading eigenimages — are shown in the bottom row, labeled with their corresponding eigenvalues. [Adapted from Medeiros et al. 2018]

Recently, a team of scientists led by Lia Medeiros (University of Arizona, University of California Santa Barbara) has demonstrated that a novel approach — principal component analysis — may be a useful tool in this process.

Principal Components

Principal component analysis is a clever mathematical approach that allows the user to convert a complicated set of observations of variables into their “principal components”. This process — commonly used in traditional statistical applications like economics and finance — can simplify the amount of information present in the observations and help identify variability.

Medeiros and collaborators demonstrate that a time sequence of simulated EHT observations — produced from high-fidelity general-relativistic magnetohydrodynamic simulations of a black hole — can be decomposed using principal component analysis into a sum of independent “eigenimages”. These eigenimages provide a means of compressing the information in the snapshots: most snapshots can be reproduced by summing just a few dozen of the leading eigenimages.

Exploring Steady and Variable Flow

A typical snapshot from a simulation (top), followed by three different reconstructions of the snapshot from the leading 10, 40, and 100 eigenimages. [Adapted from Medeiros et al. 2018]

How is this useful? If images from simulations of a black hole can be represented by sums of eigenimages, so can the actual observations produced by the EHT. By comparing the two sets of observations — real and simulated — to each other within this eigenimage framework, we’ll be able to better understand the components of what we’re observing. In addition, the mathematics of principal component analysis allow for this to work even with sparse interferometric data, as is expected with EHT observations.

Furthermore, recognizing images that aren’t represented well by the leading eigenimages is equally important. These outlier images can be indicative of flaring or otherwise variable phenomena around the black hole, and identifying moments in which this occurs will help us to better understand the physics of accretion flows around black holes.

So keep an eye out for the first images from the EHT, expected soon — there’s a good chance that principal component analysis will be helping us to make sense of them!

Citation

“Principal Component Analysis as a Tool for Characterizing Black Hole Images and Variability,” Lia Medeiros et al 2018 ApJ 864 7. http://iopscience.iop.org/article/10.3847/1538-4357/aad37a/meta

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Support for Today’s Reality of Astronomy Data”

From AAS NOVA

19 September 2018
Susanna Kohler

The Astropy project logo, overlaid on Spitzer data that was plotted using an Astropy subpackage. Astropy is a collection of software written in the Python programming language and designed for use in astronomy. [Astropy logo: Kyle Barbary, Thomas Robitaille; background image: Beerer et al. 2010]

One of the greatest misconceptions about astronomy as a profession is that we all sit alone in front of a telescope eyepiece every night, gazing at the stars. In reality, today’s observational astronomy is collaborative — and it takes the form of ones and zeros on a computer.

Two different RGB images of the region newar the Hickson 88 group, both produced with Astropy from Sloan Digital Sky Survey data. The top image uses default plot parameters; the bottom has parameters set to show a greater dynamical range. [The Astropy Collaboration et al. 2018]

SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

A Computer-Driven World

Before the days of photography, the field of astronomy did rely on lone professionals who observed the heavens through their telescopes; after that, astronomers exposed film plates to gather data. Today, astronomy is a largely computer-driven field: observations are made by telescopes that often aren’t in the same location as the astronomers, and the images the telescopes take are stored as files full of data.

Modern observational astronomers need the coding skills to process these data and turn them into images and tables. They need to use computers to fit models to the data to better understand what they’re seeing. They need to present their results via complex plots and graphs — which are again produced using code.

As a result of this reality for astronomers, the handling of astronomical data has become in large part a community-driven, collaborative process; when good ideas are shared, each individual astronomer can spend less time reinventing the wheel. It’s in this spirit that the Astropy project was first developed. In a recent publication, the Astropy collaboration has now detailed the current status of this project.

Plot of the total number of commits (contributions consisting of changes or additions) to the Astropy core package over time. [The Astropy Collaboration et al. 2018]

Pooling Resources

Many astronomers conduct their work in Python, a freely available, general-purpose programming language. Often, chunks of code that are useful to one astronomer are also useful to another — for instance, code that defines specific astronomical constants, or a module that reduces data in a certain way. Astropy is an open-source and open-development community library for such pieces of generally useful Python code for astronomy.

The Astropy project was started in 2011. Since then, the package has been used in hundreds of projects, and its scope has grown considerably. Anyone is able to contribute to this body of code, and it continues to be actively developed — as of version 2.0, the Astropy package contained over 212,244 lines of code contributed by 232 unique contributors.

Status of Astropy

In their recent publication, the authors describe some of the features currently contained in the Astropy core package — like support for coordinate transformations, reading and writing astronomical files, manipulating quantities with units attached, and modeling and visualizing data.

Spitzer data providing another example of a figure made using an Astropy subpackage, which allows for the overlay of multiple coordinate systems and customization of which ticks and labels are shown on each axis. [Beerer et al. 2010]

he Astropy collaboration also discusses their plans for the future of the project: in addition to planned changes and additions to the core package, the next major release will also include an overhaul of the Astropy educational and learning materials, designed to make it easier for new users to start taking advantage of the resources in the Astropy package.

Critical efforts like the Astropy project not only provide and develop software tools essential to modern academic research, but they also help lower the barrier to entry for the next generation of professional astronomy researchers. With such support in a collaborative community, we can only imagine what modern astronomy will look like a few generations in the future!

Citation

“The Astropy Project: Building an Open-Science Project and Status of the v2.0 Core Package,” The Astropy Collaboration et al 2018 AJ 156 123. http://iopscience.iop.org/article/10.3847/1538-3881/aabc4f/pdf

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Featured Image: Forming Disks and Rings in Galactic Nuclei “

From AAS NOVA

17 September 2018
Susanna Kohler

These dramatic simulated images reveal some of the circumnuclear gas structures that can form from the tidal disruption of molecular clouds in the nucleus of a galaxy. In a study led by Alessandro Trani (The University of Tokyo, Japan; International School for Advanced Studies, Italy; INAF-Astronomical Observatory of Padua, Italy), a team of scientists has conducted a series of simulations exploring what happens to gas in a galactic nucleus consisting of a supermassive black hole and a nuclear star cluster. Their work shows that the gas can be drawn into extended disks or compact rings, depending on whether the black hole’s influence is stronger than that of the nuclear star cluster. To read more about their outcomes, check out the paper below.

Citation

“Forming Circumnuclear Disks and Rings in Galactic Nuclei: A Competition Between Supermassive Black Hole and Nuclear Star Cluster,” Alessandro A. Trani et al 2018 ApJ 864 17.
http://iopscience.iop.org/article/10.3847/1538-4357/aad414/meta

Related journal articles
_________________________________________________
See the full article for further references with links.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “New Detections of the Milky Way’s Supermassive Black Hole”

From AAS NOVA

14 September 2018
Susanna Kohler

This far-infrared composite image of the galactic center reveals the challenge of detecting our galaxy’s supermassive black hole at these wavelengths: warm, bright dust obscures it. But by looking for variability, a team of scientists has now detected Sgr A* in far-infrared. See the image with coordinates here. [von Fellenberg et al. 2018]

A supermassive black hole lurks at the center of our galaxy — and we’re still trying to understand its structure and behavior. Now scientists have made new detections of Sgr A* in far infrared, helping us to further piece together a picture of this monster.

SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

SgrA* NASA/Chandra

Sgr A* from ESO VLT

A Missing Window

Past research suggests that most galaxies host a supermassive black hole of millions or billions of solar masses in their center — and the Milky Way is no exception.

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

Our galactic center is dominated by Sagittarius A* (Sgr A*), a black hole that weights in at about 4 million solar masses.

The electromagnetic spectrum (click to enlarge). Observations of Sgr A* have previously been lacking at far-infrared wavelengths below 250 µm. [Penubag]

We’ve observed Sgr A* across the electromagnetic spectrum through the years, noting its flux and variability in radio, millimeter and submillimeter, near-infrared, and X-ray wavelengths. A few windows are notably missing, however: dust and atmospheric obscuration have prevented observations of Sgr A* in optical and ultraviolet wavelengths, and in the far infrared at wavelengths shorter than 250 µm.

Though we’ve learned a lot about our supermassive black hole from observations, we’re still short of a fully coherent picture. What is the structure and flow of the gas and dust surrounding the black hole? What causes the various different types of emission we’ve observed from Sgr A*? Is the variability in flux we see at different wavelengths related? Or does the emission come from multiple different sources, each with its own timescale for variability?

To further build out our understanding of this mysterious source, a team of scientists led by Sebastiano von Fellenberg (Max Planck Institute for Extraterrestrial Physics, Germany) has now obtained observations of Sgr A* at 160 and 100 µm for the first time, providing new information about Sgr A* in the missing window in the far infrared.

The authors’ observations of the far-infrared variability of the region around Sgr A* (click to enlarge). Correlated variability is visible between the two observed bands, and a point source can be seen at the position of Sgr A*. [von Fellenberg et al. 2018]

Hidden Variability

Von Fellenberg and collaborators obtained these far-infrared observations not by looking directly for Sgr A* in these wavelengths, but by looking for its variability. Using ESA’s Herschel Space Observatory, the team observed the emission at 160 and 100 µm and then subtracted off the constant emission from the warm dust at the galactic center.

ESA/Herschel spacecraft active from 2009 to 2013

After correcting for systematic errors, von Fellenberg and collaborators were left with a faint signature of variable emission correlated between the two wavelengths: emission from around the black hole.

These observations have allowed the authors to place limits on Sgr A*’s far-infrared luminosity. By comparing these limits to the emission predicted by various models of accretion flow onto Sgr A*, von Fellenberg and collaborators have narrowed down the set of models that are consistent with the observations.

Though we still don’t have everything figured out about the supermassive black hole at our galaxy’s center, this work represents an important step that brings us a bit closer.

Citation

“A Detection of Sgr A* in the Far Infrared,” Sebastiano D. von Fellenberg et al 2018 ApJ 862 129. http://iopscience.iop.org/article/10.3847/1538-4357/aacd4b/meta

Related journal articles
_________________________________________________
See the full article for further references with links.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

From AAS NOVA: “Surprise Discovery of a 14-Year-Old Supernova”

From AAS NOVA

12 September 2018
Susanna Kohler

Hubble image of the galaxy NGC 1892, in which a supernova from 2004 was recently discovered. [NASA/ESA/HST]

NASA/ESA Hubble Telescope

Much of today’s astronomy happens via methodical searches, but sometimes serendipitous discoveries still surprise us. Such is the case with the transient CGS2004A, a possible supernova recently detected in a galaxy nearly 50 million light-years away.

Observing Explosions

Supernovae — some of the brightest phenomena in our universe — are vast explosions thought to mark the destruction of stars in the end stages of their evolution.

The history of supernova observations is long: the first recorded supernova was seen in China in 185 AD! Because supernovae are scarce (there are perhaps 1–3 per century in the Milky Way) and their brightest stages of are short-lived (lasting just a few months), only a handful of supernova were spotted by naked eye through the ages. The invention of the telescope, however, changed this: as technology improved, astronomers became able to observe bright supernovae in galaxies beyond the Milky Way.

Chronological observations of NGC 1892. From the top, a Hubble image from 2001, the CGS image from 2004, Stockler de Moraes’s image from 2017, and a Magellan image from 2018. The transient is visible only in the 2004 CGS image. [Guillochon et al. 2018]

Today, around 50,000 supernovae have been observed. The field has been vastly expanded by recent automated sky surveys that methodically hunt for transients. Nonetheless, intrepid individual astronomers still contribute to this scene — as evidenced by the recent discovery by Brazilian amateur astronomer Jorge Stockler de Moraes.

An Unexpected Find

In January of 2017, Stockler de Moraes imaged the distant galaxy NGC 1892 using a 12-inch diameter telescope. When he later compared his image to an archival image from 2004 of the same galaxy, taken as part of the Carnegie-Irvine Galaxy Survey (CGS), he discovered a distinct difference between the two photos: a bright source was present in the archival image that wasn’t visible in his recent photo.

Stockler de Moraes next contacted astronomer James Guillochon (Harvard Center for Astrophysics), who first eliminated possible alternate explanations for the source — such as minor planets in our solar system that might have coincided with NGC 1892 at the time. Guillochon then worked with a team of collaborators to explore other images of the galaxy and conduct follow-up imaging, as well as analyze the transient in the CGS image.

Core Collapse

The transient — labeled CGS2004A — was found to be absent in all additional images the authors explored, both in years before and after the CGS observation. Guillochon and collaborators’ photometric analysis of the transient and our knowledge of the nature of NGC 1892, a massive, star-forming galaxy, further suggest that this transient was likely a Type IIP supernova, caused when the core of a massive star (perhaps 8–50 solar masses) suddenly collapses.

Based on the authors’ analysis, it would seem that Stockler de Moraes serendipitously discovered a stellar explosion that went unnoticed 14 years ago. Discoveries such as these help us to continue to expand our understanding of how stars evolve throughout the universe.

Bonus

For a cool way to experience the history of supernova detections over time, check out the video by astronomer Greg Salvesen below. Chronological discoveries of supernovae are displayed both visually and using sound, for the time period of 1950 to the start of 2018. You can skip ahead to ~1990 to see detection rates pick up as more surveys come online! Data is from the Open Supernova Catalog by Guillochon et al.

Citation

“Serendipitous Discovery of a 14-year-old Supernova at 16 Mpc,” James Guillochon et al 2018 Res. Notes AAS 2 165.http://iopscience.iop.org/article/10.3847/2515-5172/aade89/meta

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009