From AAS NOVA: “Confirming New Physics in Space”

From AAS NOVA

24 January 2020
Susanna Kohler

Hubble image of the planetary nebula NGC 5189. A recent study has confirmed a new atomic process at work in nebulae such as this one. [NASA, ESA and the Hubble Heritage Team (STScI/AURA)]

Not all laboratory astrophysics occurs in labs down here on Earth; sometimes, the lab is in space! A new study has used a space laboratory to confirm a new atomic process — with far-reaching implications.

The Cat’s Eye planetary nebula, as imaged in X-rays and optical light. [X-ray: NASA/CXC/SAO; Optical: NASA/STScI]

NASA/ESA Hubble Telescope

Balancing a Plasma

Throughout our universe, cosmic soups of electrons and ions — astrophysical nebulae — fill the spaces surrounding dying stars, hot and compact binaries, and even supermassive black holes. The atoms in these nebulae cycle within a delicate balance: they are ionized (electrons are torn off) by the high-energy photons emitted from the hot nearby sources, and then they recombine (electrons are recaptured), emitting glowing radiation in the process.

After many years of research into atomic processes, we thought that we’d pretty well pinned down the ways in which this photoionization and recombination takes place. This is crucial, since these rates go into models that we use to determine abundances — which, in turn, informs our understanding of stellar evolution, nucleosynthesis, galactic composition and kinematics, and cosmology.

But what if we’re missing something?

A New Process

A diagram of how Rydberg Enhanced Recombination works. [Nemer et al. 2019]

In 2010, a team of scientists proposed exactly this: that we’re missing an additional type of recombination process that occurs frequently in astrophysical plasmas throughout the universe.

The catch? This type of recombination — which they termed Rydberg Enhanced Recombination, or RER — had never before been detected, and it’s effectively impossible to study in Earth-based laboratories. Only in cold, low-density cosmic environments like astrophysical nebulae do the conditions necessary for RER exist.

Laboratories in Space

When Earth-based labs fail, it’s time to look to space! A team of scientists led by Ahmad Nemer (Auburn University; Princeton University) recently went on the hunt for astrophysical laboratories showing evidence of RER.

First, Nemer and collaborators developed detailed models of how RER would work, under what conditions it would be effective, and what observable spectral lines this process would produce.

Illustration of a symbiotic binary system, consisting of a white dwarf and a red giant. [NASA, ESA, and D. Berry (STScI)]

With sample spectra in hand, they then explored the high-resolution optical spectra of several planetary nebulae (the clouds of ionized plasma that surround dying, low-mass stars) and ultraviolet spectra of symbiotic binaries (systems where ionized plasma surrounds a white dwarf accreting mass from a red giant).

Time for an Update

Space lab success! In eight of the planetary nebulae and one of the symbiotic binaries, the authors found spectral lines that provide evidence of the RER process at work, with relative strengths that agree nicely with predictions.

This confirmation of a predicted new atomic process represents a remarkable discovery with far-reaching implications. Nemer and collaborators show that the addition of RER contributions into our current models of ionization balance makes a significant difference in estimated elemental abundances of astrophysical nebulae — which means we may have a lot of work ahead of us to update our past research!

Thanks to the power of laboratories in space, however, we now have a clearer idea of what we’ve been missing.

Citation

“First Evidence of Enhanced Recombination in Astrophysical Environments and the Implications for Plasma Diagnostics,” A. Nemer et al 2019 ApJL 887 L9.

https://iopscience.iop.org/article/10.3847/2041-8213/ab5954

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: “Connecting the Universe’s Large and Small Scales”

From AAS NOVA

30 December 2019
Susanna Kohler

Artist’s impression of the first stars in the universe. A new study supports the idea that some of these large stars may have collapsed into GEODEs — dark-energy-filled black holes. [NASA/WMAP Science Team]

NASA/WMAP 2001 to 2010

Implications of Symmetry and Pressure in Friedmann Cosmology. I. Formalism

Published August 2019

Main takeaway:

Two scientists at University of Hawai’i at Mānoa, Kevin Croker and Joel Weiner, have reexplored Friedmann’s equations — the set of equations that describe the expansion of the universe — under a different set of fundamental assumptions. Using their revised formalism, they show that the universe’s growth rate can be influenced by the relatively small pressure contributions of compact objects left behind after a star’s death.

According to the authors’ calculations, contributions from compact, relativistic objects like neutron stars, illustrated above, could affect the growth rate of the universe. [NASA/Goddard Space Flight Center/Dana Berry]

Why it’s interesting:

In previous studies, it’s been assumed that the universe’s matter is all alike and evenly distributed — an assumption that allows us to ignore the details of small structures like stars and galaxies when calculating the evolution of the universe as a whole. But Croker and Weiner’s calculations shows that the averaged contributions of massive, compact objects could affect the universe’s expansion rate after all — and in exchange, the universe’s evolution may affect the energy gain or loss of these compact objects over time. This work provides a new link between the small-scale structures and large-scale evolution of the universe.

What this work says about dark-matter-filled black holes:

Croker and Weiner’s model has an interesting side note: it has revived interest in an alternative picture of how we conceive of black holes. In the 1960s, Russian physicist Erast Gliner proposed that large stars would collapse into GEODEs — Generic Objects of Dark Energy — at the ends of their lifetimes. These objects would look like black holes from the outside, but on the inside, they would contain a bubble of dark energy instead of a singularity. Croker and Weiner have revived Gliner’s theory by demonstrating that if just a fraction of the oldest stars in our universe collapsed into GEODEs instead of black holes, the averaged contribution of these objects today would naturally produce the required uniform dark energy to produce the expansion of the universe we observe. In addition, collisions of GEODEs could naturally explain LIGO’s gravitational-wave observations.

Citation

K. S. Croker and J. L. Weiner 2019 ApJ 882 19.
https://iopscience.iop.org/article/10.3847/1538-4357/ab32da

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: “A Giant Planet Around an Evolved Binary”

From AAS NOVA

17 December 2019
Susanna Kohler

Illustration of the planetary system KIC 10544976, in which a giant planet orbits a binary white dwarf and M dwarf. [Leandro Almeida]

In a study led by Leonardo Almeida (Federal University of Rio Grande do Norte and University of São Paulo, Brazil), scientists announce evidence for a 13-Jupiter-mass planet around an evolved binary system, KIC 10544976, that consists of a white dwarf and a red dwarf star orbiting each other once every 0.35 days.

Why it’s interesting:

This is the first planet found orbiting an evolved binary like this one, and it raises questions as to how it formed. Was the planet born at the same time as the stars, and somehow survived the end of life of the binary member that evolved into a white dwarf? Or was the planet instead born later, out of the gas ejected by this star as it died? By studying the KIC 10544976 planet with next generation telescopes, we should be able to answer this question.

How the planet was discovered:

Observations of the eclipsing binary stars show timing variations in the eclipses. This change in orbit could be caused by one of two things: either the gravitational tug of an additional unseen, massive body, or period fluctuations in the magnetic field of the red dwarf. By studying the magnetic activity cycle for the red dwarf using years of flare and starspot data, Almeida and collaborators were able to rule out the hypothesis that magnetic activity caused the eclipse timing variations. This made the presence of a giant planet the most likely explanation.

Telescopes involved with this project

Isaac Newton Group of Telescopes located at Roque de los Muchachos Observatory on La Palma in the Canary Islands Altitude 2,396 m (7,861 ft)

ING 4.2 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

Citation

L. A. Almeida et al 2019 AJ 157 150.
https://iopscience.iop.org/article/10.3847/1538-3881/ab0963

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: “An Extreme Pulsar Seen in Gamma Rays”

From AAS NOVA

11 December 2019
Susanna Kohler

Artist’s illustration of a pulsar (left) and its small stellar companion (right), viewed within their orbital plane. [NASA Goddard SFC/Cruz deWilde]

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.

One of the fastest spinning radio pulsars known has now been detected to pulse in gamma rays, too. What can we learn about this extreme pulsar from new observations?

Artist’s illustration of a pulsar, a fast-spinning, magnetized neutron star. [NASA]

Pushing the Record for Spin

Pulsars are rapidly spinning, magnetized neutron stars left behind at the end of a star’s lifetime. Pulsar J0952-0607, a pulsar in a binary orbit with a very low-mass companion star, has the second-fastest known pulsar spin, rotating 707 times each second. For comparison, that’s about 70 times faster spin than the fastest helicopter rotors — and it’s an object that’s 10 km across and weighs more than the Sun!

As it spins, PSR J0952-0607 flashes a beam of radio waves across the path of the Earth, radiating from a hot spot on its surface. In a recent study, a team of scientists led by Lars Nieder (Albert Einstein Institute and Leibniz University Hannover, Germany) have now hunted through years of data from the Fermi Gamma-ray Space Telescope to see if we can spot pulsations from a gamma-ray beam as well.

NASA/Fermi LAT

NASA/Fermi Gamma Ray Space Telescope

Finding High-Energy Pulses

The radio observations of PSR J0952-0607’s pulsations span only 100 days, which isn’t long enough to precisely constrain its properties. The Fermi Gamma-ray Space Telescope launched in 2008, and its Large Area Telescope (LAT) has been providing all-sky images on a regular basis since then. Nieder and collaborators reasoned that if they could spot PSR J0952-0607 in gamma rays in the Fermi LAT data, then they’d be able to observe the pulsar over a much longer baseline than its radio observations provide.

The catch? PSR J0952-0607 is very faint in gamma-rays — which is why its pulsations weren’t previously detected. Nieder and collaborators had to develop novel search and timing methods with greater sensitivity, ultimately using the computational equivalent of 24 years on a single-core computer to search for a signal. Their efforts paid off, however — they managed to detect faint gamma-ray pulsations from PSR J0952-0607 spanning from July 2011 to the end of the dataset in January 2017.

Plot of the spin-down rate vs. the spin for the known pulsar population outside of globular clusters. PSR J0952-0607 is marked by an orange star. [Nieder et al. 2019]

Some Answers and Some New Puzzles

From the gamma-ray observations, Nieder and collaborators were able to measure a precise spin-down rate for the pulsar (it slows by less than 4.6 x 10-21 seconds each second), as well as other properties. PSR J0952-0607’s inferred magnetic field is among the 10 lowest magnetic fields measured for pulsars — an extreme that is predicted by theory based on this pulsar’s remarkably fast spin.

Though we’ve gained a lot of information about PSR J0952-0607 from its gamma-ray pulsations, new mysteries have also been introduced. The fact that its pulsations are undetectable before July 2011 is one of these — could the pulsar’s flux have changed? Or its orbit around its companion star? We’ll need more data to be able to solve this puzzle.

We still have more to learn about PSR J0952-0607, but the newly discovered gamma-ray pulsations have provided us with unique insight into the extremes that arise when compact astrophysical bodies spin at such high speeds. With luck, future observations of this pulsar — and others like it — will help us to further probe the physics of these unusual sources.

Citation

“Detection and Timing of Gamma-Ray Pulsations from the 707 Hz Pulsar J0952−0607,” L. Nieder et al 2019 ApJ 883 42.
https://iopscience.iop.org/article/10.3847/1538-4357/ab357e

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: “Mass-ive Implications for Exoplanetary Atmospheres”

From AAS NOVA

9 December 2019
Tarini Konchady

Artist’s impression of an extrasolar planet system. [R. Hurt (IPAC)/NASA/JPL-Caltech]

One of the goals of the Transiting Exoplanet Survey Satellite (TESS) is to identify exoplanets whose atmospheres can be characterized by other telescopes.

NASA/MIT TESS replaced Kepler in search for exoplanets

Part of this process entails measuring planetary masses to some degree of precision. So just how well do we need to know an exoplanet’s mass to understand its atmosphere?

The Use of Transmission Spectra

One way to study the atmosphere of an exoplanet is to observe the light from its host star that passes through the planet’s atmosphere. Comparing the resulting spectrum — called a transmission spectrum — with the spectrum of the host star alone can tell us about what’s in the planet’s atmosphere.

A planet’s mass plays an important role in how far its atmosphere extends. This has prompted studies on whether a planet’s mass could be inferred from its transmission spectrum alone. In some cases, this approach works. But in other cases, the transmission spectra of very different planets can appear to be alike.

The precision of exoplanet mass measurements versus their most likely mass. The seven planets used in this study are highlighted. [Adapted from Batalha et al. 2019]

So should we know the mass of a planet before trying to characterize its atmosphere? If so, how well? And how do these answers change for different types of planets? Natasha Batalha (University of California, Santa Cruz) and collaborators attempt to tackle these questions with simulated James Webb Space Telescope (JWST) transmission spectra.

Seven Special Planets

For their study, Batalha and collaborators chose seven known planets that span the gamut of exoplanets we’ve observed. Their sample included three hot Jupiters (WASP-17b, HAT-P-1b, WASP-12b), three Neptune-like planets (HAT-P-26 b, GJ 436b, GJ 1214b), and one Earth-like planet (TRAPPIST-1e).

To simulate transmission spectra, the authors started with models that are consistent with Hubble spectroscopy of their chosen planets. They then used these models to simulate the analogous JWST spectra.

Aside from mass, the sample planets also varied in composition. Their host stars are also different, meaning that in real life the JWST would have to adopt different observing strategies to get quality transmission spectra.

The accuracy with which different atmospheric properties are recovered from the simulated transmission spectra. From top left, clockwise: temperature, metallicity (the abundance of elements that are not hydrogen or helium), radius, and mass. The shaded regions correspond to mass being known and the unfilled regions correspond to mass not being known. The colors of the curves indicate different planets. [Batalha et al. 2019]

A Matter of Caution

To test what role mass played in the usefulness of transmission spectra, the authors attempted to measure atmospheric properties from their modeled spectra. They tried different precisions on mass (how far off the assumed mass could be from the true mass) as well as not knowing a planet’s mass at all.

The authors found that transmission spectra alone could not reliably characterize a planet’s atmosphere. Hot Jupiters required the loosest mass constraints to infer atmospheric properties, though cloud cover — such as in the case of WASP-12b — could make that untrue. For the other Neptunes and the Earth-like planet, mass had to be known with at least a 50% precision to get accurate atmospheric properties.

A recurring theme was that a mass measurement is necessary to distinguish one planet from others with similar transmission spectra. To this end, the authors recommend that any planets selected for atmospheric characterization have their mass known to at least 50% precision.

One of TESS’s goals is to measure the mass of fifty Earth-sized planets, and Batalha and collaborators have set a benchmark for those measurements. This sort of groundwork is critical to exoplanet science and should contribute to great results not too long from now!

Citation

“The Precision of Mass Measurements Required for Robust Atmospheric Characterization of Transiting Exoplanets,” Natasha E. Batalha et al 2019 ApJL 885 L25.
https://iopscience.iop.org/article/10.3847/2041-8213/ab4909

See the full article here .
See also from UCSC “From UC Santa Cruz and Carnegie Institution for Science: “Composition of gas giant planets not determined by host star, study finds”

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: “Climates of Distant Terrestrial Worlds”

From AAS NOVA

27 November 2019
Susanna Kohler

Artist’s illustration of an M-dwarf star surrounded by three planets. [NASA/JPL-Caltech]

What determines the climate of an Earth-like planet orbiting its host star? And how is that climate affected by the type of star the planet orbits? A new study explores how distant terrestrial worlds are shaped by their hosts.

Radiation In, Radiation Out

The climate for a planet like Earth is largely set by the delicate balance between incoming radiation from the planet’s star, and outgoing radiation in the form of heat emitted into space. The amount of energy absorbed, reflected, and emitted by a planet’s surface and atmosphere dictate how this balance plays out.

Diagram describing the annual mean energy budget for a planet orbiting a G dwarf star.[Adapted from Shields et al. 2019]

The pathways that govern this global energy budget for our own planet have been worked out through many decades of modeling and analysis of observations — to the point where we can identify sources of imbalance in the Earth’s system, like those currently caused by anthropogenic CO2 emissions.

But these climate models don’t apply directly to other planets, because the factors that determine a planet’s global energy budget all depend on the wavelength distribution of incoming light. Since stars of different temperatures emit varying amounts of radiation at different wavelengths, models that describe the energy budget for a planet around a Sun-like G dwarf won’t accurately describe a planet around a cooler M dwarf or hotter F dwarf.

So how do the climates of distant, Earth-like worlds change when orbiting a different type of host star? A team of scientists led by Aomawa Shields (University of California, Irvine) has now used detailed 3D global climate models to find out.

A Difference of Hosts

Shields and collaborators’ models of terrestrial planets take into account details like the interaction between the incoming host star’s radiation and gases like CO2 and H2O in the planet’s atmosphere, as well as with icy and snowy surfaces on the ground.

Plot of the global mean surface temperature as a function of the amount of incoming stellar radiation at the top of the planet’s atmosphere, shown for a planet orbiting an F dwarf (blue triangles), a G dwarf (black plus symobls), and an M dwarf (red x symbols). [Adapted from Shields et al. 2019]

The authors show that M-dwarf planets absorb more of their hosts’ radiation, both in their atmospheres and their surfaces, whereas F-dwarf planets absorb less. As a result, a planet can have a climate similar to that of modern-day Earth if it’s receiving current solar amounts of incoming radiation from a G-dwarf star — but to achieve the same climate around an M-dwarf star, it would need to receive 12% less incoming radiation. Around an F-dwarf star, it would need to receive 8% more.

What about rotation? The above models assumed that the planets all had 24-hour rotation rates, but Shields and collaborators also test how this compares to a tidally locked planet that always shows the same face to its host. For an M-dwarf host, a tidally locked planet has lower minimum and maximum dayside temperatures when compared with a planet with a 24-hour rotation period; the average dayside temperature is around 37 K colder on the tidally locked planet.

As we continue to discover more planets around a variety of stars, a constant question is whether these distant worlds have the potential to support life. Understanding how these planets’ global climates are shaped by their host stars is an important part of this exploration!

Citation

“Energy Budgets for Terrestrial Extrasolar Planets,” Aomawa L. Shields et al 2019 ApJL 884 L2.
https://iopscience.iop.org/article/10.3847/2041-8213/ab44ce

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: “Fantastically Fast Transients and How They Happen”

From AAS NOVA

22 November 2019
Tarini Konchady

An example of the appearance (left) and disappearance (right) of a fast transient — in this case, the optical counterpart of a binary neutron star merger. A new study explores a similarly rapid fast transient that may have a very different origin. [Soares-Santos et al. 2017]

A supernova-like transient was observed to decline stupendously fast. What could have caused it?

Fast Transients

“Fast transients” are objects whose brightness rises and then falls drastically, usually on the order of weeks. They are not regularly varying objects; they have more in common with supernovae, which brighten once and then fade. However, fast transients change more rapidly than supernovae do, suggesting they have different explosive progenitors.

With the advent of large astronomical surveys, fast transients are spotted more often now than ever before. The “fastest” optical fast transient is kilonova AT2017gfo — the result of the first observed binary neutron star merger. A recent study by Owen McBrien (Queen’s University Belfast) and collaborators discusses a transient that’s right on the heels of AT2017gfo in terms of the speed of its variation: a supernova-like object named SN2018kzr.

The host galaxy of SN2018kzr, as seen more than two months after the transient appeared. The image was constructed using data taken by the ESO (European Southern Observatory) Faint Object Spectrograph and Camera on the New Technology Telescope. [Adapted from McBrien et al. 2019]

ESO Faint Object Spectrograph and Camera 2 (EFOSC2)
on the NTT

ESO/NTT at Cerro La Silla, Chile, at an altitude of 2400 metres

Magnetars and Nickel

SN2018kzr was discovered independently by the Zwicky Transient Factory and the Asteroid Terrestrial-impact Last Alert System.

Zwicky Transient Facility (ZTF) instrument installed on the 1.2m diameter Samuel Oschin Telescope at Palomar Observatory in California. Courtesy Caltech Optical Observatories

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

Observers were tipped off by its rapid brightening, which took place over hours. SN2018kzr was then observed extensively over the next two weeks by multiple observatories, yielding a wealth of photometric and spectroscopic data. It began declining in brightness the same night it was first detected.

To explain SN2018kzr’s rise and fall, McBrien and collaborators consider mechanisms that have previously been used for fast transients. They start with the reasonable assumption that nickel-56 is involved. The isotope nickel-56 can form in the explosions associated with fast transients and supernovae, and its radioactive decay can contribute greatly to a transient’s brightness. However, SN2018kzr dims too rapidly for it to be explained by nickel-56 alone, and the decay of other radioactive isotopes don’t explain observations either.

One solution is to tweak the progenitor scenario to include a massive remnant: a rotating neutron star with a strong magnetic field, known as a magnetar. A magnetar can contribute to the energy put out by SN2018kzr by slowing its own rotation. When coupled with nickel-56 decay, a magnetar’s spin-down could explain the shape of SN2018kzr’s light curve.

Fits to the light curve of SN2018kzr assuming different progenitor scenarios. The red points are associated with SN2018kzr and the white diamonds are associated with another fast transient, SN2005ek. SN2005ek is better fit by the He star model, while SN2018kzr is better fit by the nickel-56–magnetar scenario. [Adapted from McBrien et al. 2019]

Assuming that nickel-56 and a magnetar are involved in the progenitor of SN2018kzr, the authors present three possible scenarios: the core-collapse of a helium-rich star, the collapse of a white dwarf that’s accreted too much matter (accretion induced collapse, or AIC), and the merger of a white dwarf and a neutron star.

The first scenario isn’t favored since any remnant it produces wouldn’t rotate fast enough to explain SN2018kzr’s rapid decline. The authors favor the other scenarios, though the AIC model is on shaky ground based on previous studies.

The more fast transients we discover, the better our understanding becomes of how they form. Stay tuned!
Citation

“SN2018kzr: a rapidly declining transient from the destruction of a white dwarf,” Owen R. McBrien et al 2019 ApJL 885 L23.
https://iopscience.iop.org/article/10.3847/2041-8213/ab4dae

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: “Hunting for a Dark Matter Wake”

From AAS NOVA

13 November 2019
Susanna Kohler

The Large Magellanic Cloud is the Milky Way’s most massive satellite. What evidence has this galaxy left behind as it plows through the Milky Way’s dark matter halo? [ESO/VMC Survey]

As the Large Magellanic Cloud plows through the Milky Way’s dark matter halo, it may leave telltale signs of its passage. A recent study explores whether we’ll be able to spot this evidence — and what it can tell us about our galaxy and the nature of dark matter.

The Large and Small Magellanic clouds, as observed from Earth. [ESO/S. Brunier]

The Milky Way’s Large Companion

The Milky Way is far from lonely. Dozens of smaller satellite-galaxy companions orbit around our galaxy, charging through its larger dark matter halo. The most massive of these is the Large Magellanic Cloud (LMC), a galaxy of perhaps 10 or 100 billion solar masses that’s about 14,000 light-years across.

Studies suggest that the LMC is on its first pass around the Milky Way, traveling on a highly eccentric orbit; it likely only first got close to our galaxy (within about 200 kpc, or 650,000 light-years) about two billion years ago.

There are still many uncertainties about this satellite and its travels, however. How massive, exactly, is the LMC? What does its past orbit look like? And how has it interacted with our galaxy’s dark matter halo, which it’s passing through?

Density perturbations caused by the LMC’s motion for one of the authors’ Milky Way models. The Milky Way’s disk is in the x–y plane; the black curve traces the LMC’s past orbital path and the red star indicates its current position. Three primary overdense/underdense features are visible as signatures of the LMC’s wake. [Adapted from Garavito-Camargo et al. 2019]

A Telltale Trail

A team of scientists led by Nicolas Garavito-Camargo (Steward Observatory, University of Arizona) thinks there may be evidence we can use to answer these questions.

Like a boat, the LMC should generate a wake as it plows through the Milky Way’s dark matter halo. This wake is caused by gravitational interactions between the satellite and dark matter particles that drag at the LMC, causing the galaxy to lose angular momentum as it orbits.

The perturbations that make up this wake — overdensities and underdensities in the dark matter and stellar distribution in the halo — are signatures that we can predict and hunt for. In a new study, Garavito-Camargo and collaborators use high-resolution N-body simulations to explore the motion of the LMC through the Milky Way’s halo and examine the perturbations caused by this charging satellite.

Spotting the Evidence of Passage

The authors find that the LMC’s motion produces a pronounced dark matter wake that can be decomposed into three parts:

Transient response, a trailing wake of overdensity behind the satellite that traces its orbital history
Global underdensity, a large underdense region south of the transient response
Collective response, an extended overdensity leading the LMC in the galactic north

These features in the dark-matter distribution are echoed in how stars are distributed in the regions, and the stars should also show distinctive kinematic signatures.

Observing strategies for identifying the LMC’s wake using stellar densities. To avoid confusion with the Sagittarius stellar stream (the prominent yellow, orange, and red points indicated), the authors identify several regions for observation (colored rectangles) away from the stream where the wake should be detectable. [Garavito-Camargo et al. 2019]

Garavito-Camargo and collaborators outline an observing strategy to spot the predicted overdensities and underdensities of the wake, and they show that the detection of just 20–30 stars in specific regions could provide useful confirmation of their models. The measurements needed should be achievable with current and upcoming stellar surveys.

What can we learn from these observations? The detection of the LMC’s wake will track its past orbit, which will provide an indirect measure of our own galaxy’s mass. The specifics of the LMC’s motion will also better constrain the satellite’s mass, as well as provide clues as to the nature of the dark-matter particles that drag on it.

Citation

“Hunting for the Dark Matter Wake Induced by the Large Magellanic Cloud,” Nicolas Garavito-Camargo et al 2019 ApJ 884 51.

https://iopscience.iop.org/article/10.3847/1538-4357/ab32eb

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: “A New Measurement of Turbulence”

From AAS NOVA

11 November 2019
Susanna Kohler

Many astrophysical plasmas demonstrate turbulence, like the gas of the Crab Nebula, pictured here. A new study has brought us one step closer to understanding this complex physical process. [NASA, ESA, J. Hester and A. Loll (Arizona State University)]

The same physical phenomenon that causes bumpy airplane rides also pervades our universe, jumbling stellar atmospheres, interstellar clouds, and even the magnetized sheath surrounding the Earth. Now, a new study brings us a little closer to understanding turbulence.

This image captures the transition between laminar and turbulent flow in the convection plume above a candle flame.

A Complex Phenomenon

Have you ever watched the entrancing wisps of smoke rising above a candle flame? What you’re looking at is turbulence — and despite this phenomenon’s prevalence throughout the universe, a complete description of turbulence remains one of the unsolved problems in physics.

The difficulty is that turbulent motion — characterized by rapid and chaotic fluctuations of fluid properties — is incredibly complex. Turbulence begins when energy is injected on large scales, causing field-level fluctuations. This energy then cascades down to smaller and smaller scales, creating chaotic motions all the way down to microscales. When the energy reaches small enough scales, it can dissipate, accelerating individual particles and converting into heat.

But scientists don’t fully understand the physical mechanisms at work in turbulence that inject the energy, transfer it to smaller scales, and eventually dissipate it. Worse yet, these processes take a different form when we’re no longer talking about fluids, but instead about astrophysical plasmas.

Plasmas, Plasmas Everywhere

Astrophysical plasmas are soups of ionized gas found everywhere from supernova remnants to the compressed solar wind surrounding the Earth in its magnetosheath — and in these plasmas, energy could be dissipated through a variety of mechanisms related to interactions between particles and waves.

This diagram of the Earth’s magnetosphere shows the location of the magnetosheath, the region behind the bow shock where the compressed solar wind detours around the Earth. [NASA/Goddard/Aaron Kaase]

How can we tell which mechanisms are at work? The key is to explore the rate at which turbulence in a plasma is dissipated across different length scales. In a recent study, a team of scientists led by Jiansen He (Peking University, China) has now developed a new approach to examine this spectrum and applied it within the Earth’s magnetosheath.

Measuring a Fluctuating Environment

The authors’ approach takes advantage of unprecedented, high-quality measurements made by the Magnetospheric Multiscale mission, a constellation of four spacecraft exploring the plasma environment around the Earth. As these spacecraft — separated by a distance of about 10 km — pass through magnetosheath plasma, they make measurements of the three-dimensional electric and magnetic fields, tracking the field fluctuations caused by turbulence.

Artist depiction of the Magnetospheric Multiscale Mission spacecraft. [NASA/GSFC]

He and collaborators present a method that uses these measured fluctuations to investigate how the dissipation rate is distributed across various length scales within the plasma. This spectrum of dissipation rates can then tell us which physical processes are most likely at play, driving the dissipation.

While we still have a lot to learn, He and collaborators’ work indicates that ion cyclotron waves — waves generated when ions oscillate in a magnetized plasma — play an important role in dissipating turbulent energy in the Earth’s magnetosheath.

More importantly, the authors’ approach for measuring the dissipation rates at different scales can be widely applied to different space plasma environments — so we can hope for more insight into turbulence in space in the future!

Citation

“Direct Measurement of the Dissipation Rate Spectrum around Ion Kinetic Scales in Space Plasma Turbulence,” Jiansen He et al 2019 ApJ 880 121.
https://iopscience.iop.org/article/10.3847/1538-4357/ab2a79

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: “A Standard of Black Hole Mergers”

From AAS NOVA

8 November 2019
Tarini Konchady

A simulated image of two black holes merging. [SXS]

Being able to make precise measurements of distances and redshifts will help us understand how the universe is evolving. With the advent of gravitational wave observatories, we can make these measurements by using black holes in a very different way than before.

MIT /Caltech Advanced aLigo

VIRGO Gravitational Wave interferometer, near Pisa, Italy

Standard Sirens

To measure how the universe is expanding, we need to simultaneously obtain the distances and redshifts to sources. When it comes to measuring large distances in space, astronomers have typically leaned on “standard candles” — objects whose intrinsic brightness is known. The dimmer a standard candle appears, the farther away it is.

Merging binary black holes (BBHs) can serve as standard candles, in a way. When compact objects like black holes merge, they produce gravitational waves, which can be picked up by observatories like the Laser Interferometer Gravitational-Wave Observatory (LIGO). The emitted gravitational waves have a characteristic energy, meaning that these mergers could be used to measure distances as “standard sirens”.

The trouble comes when trying to simultaneously measure the redshift of these sources. The gravitational wave detection on Earth gives us a mass measurement for the black holes that’s a combination of their redshift and their true masses in the source frame. If we know the true masses, we can disentangle these variables and determine the redshift. To achieve this, Will Farr (Stony Brook University and Flatiron Institute) and collaborators propose using a particular constraint on the masses of BBHs.

True black hole mass (not measured mass) versus redshift as obtained from one year of simulated BBH merger observations. The blue line indicates the maximum mass of black holes as set by PISNs, with the dark and light bars showing the confidence intervals. [Farr et al. 2019]

Capping Masses

When we model the population of merging black holes we’ve detected via gravitational wave observations, we see a drop-off in black hole mass above 45 solar masses. Farr and collaborators suggest this upper limit could be tied to one specific route of black hole creation: pair instability supernovae (PISNs).

Only massive stars can die as PISNs. In these events, the core of a star gets hot enough to allow electron–positron pairs to pop into existence, which lowers the star’s internal pressure enough for gravity to trigger the trademark explosion of a supernova. The remnants left behind by PISNs peak in mass around 45 solar masses.

By taking advantage of the mass scale imprinted on the population of BBH mergers by the PISN process, Farr and collaborators argue, we can extract redshifts from our detector measurements. Simulating 5 years of detections, the authors show that we could potentially constrain the Hubble parameter — our measurement of the expansion of the universe — at a specific redshift to within an impressive 2.9%.

Distributions of the Hubble parameter at a redshift of 0.8 as estimated by one year of observations (blue) and five years of observations (orange). The true value of the Hubble parameter at that redshift is indicated by the black vertical line. [Adapted from Farr et al. 2019]

Paring Down Parameters

The authors find that BBHs are most useful for constraining the Hubble parameter at a redshift of z = 0.8 (redshifts that can be explored with the current capabilities of gravitational wave observatories are between z = 0 and 1.5). This is because at that redshift the models peg the uncertainty on the Hubble parameter at a minimum. Additionally, the uncertainty is halved when going from one year of observations to five years.

The authors note that a change of 1–2 solar masses in their maximum black hole mass does not change their results drastically. Their method would also work with a different maximum mass — so long as there is some mass scale, BBH mergers can be used to measure distances.

New gravitational-wave detectors will extend our sample of BBH mergers enormously. With a larger sample and a better understanding of the utility of black holes, we will be closer to pinning down the fate of the universe.

Citation

“A Future Percent-level Measurement of the Hubble Expansion at Redshift 0.8 with Advanced LIGO,” Will M. Farr et al 2019 ApJL 883 L42.

https://iopscience.iop.org/article/10.3847/2041-8213/ab4284

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