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Space News Update — June 23, 2020 —

Contents

In the News

Story 1:

Proposed NASA Mission Would Visit Neptune's Curious Moon Triton

Story 2:

X-Rays from a Newborn Star Hint at Our Sun's Earliest Days

Story 3:

Supergiant Atmosphere of Antares Revealed by Radio Telescopes

Departments

The Night Sky

ISS Sighting Opportunities

NASA-TV Highlights

Space Calendar

Food for Thought

Space Image of the Week

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1. Proposed NASA Mission Would Visit Neptune's Curious Moon Triton

This global color mosaic of Neptune's moon Triton was taken in 1989 by Voyager 2 during its flyby of the Neptune

system. Credits: NASA/JPL-Caltech NASA/JPL/USGS

When NASA's Voyager 2 spacecraft flew by Neptune's strange moon Triton three decades ago, it wrote a planetary

science cliffhanger.

Voyager 2 is the only spacecraft ever to have flown past Neptune, and it left a lot of unanswered questions. The

views were as stunning as they were puzzling, revealing massive, dark plumes of icy material spraying out from

Triton's surface. But how? Images showed that the icy landscape was young and had been resurfaced over and

over with fresh material. But what material, and from where?

How could an ancient moon six times farther from the Sun than Jupiter still be active? Is there something in its

interior that is still warm enough to drive this activity?

A new mission competing for selection under NASA's Discovery Program aims to untangle these mysteries. Called

Trident, like the three-pronged spear carried by the ancient Roman sea god Neptune, the team is one of four that is

developing concept studies for new missions. Up to two will be selected by summer 2021 to become a full-fledged

mission and will launch later in the decade.

Investigating how Triton has changed over time would give scientists a better understanding of how solar system

bodies evolve and work.

The oddities of Triton could fill an almanac: As Neptune rotates, Triton orbits in the opposite direction. No other

large moon in the solar system does that. And Triton’s orbit lies at an extreme tilt, offset from Neptune's equator by

23 degrees. About three-quarters the diameter of our own Moon, Triton isn't where it used to be, either. It likely

migrated from the Kuiper Belt, a region beyond Neptune of icy bodies left over from the early solar system.

Triton has an unusual atmosphere, too: Filled with charged particles, a layer called the ionosphere is 10 times more

active than that of any other moon in the solar system.

That last trait is especially strange, because ionospheres generally are charged by solar energy. But Triton and

Neptune are far from the Sun — 30 times farther from the Sun than Earth, so some other energy source must be at

work. (It takes 165 Earth years for Neptune to complete one orbit around the Sun.)

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A new Discovery mission proposal, Trident would explore Neptune's largest moon, Triton, which is potentially an ocean

world with liquid water under its icy crust. Trident aims to answer the questions outlined in the graphic illustration above.

Credits: NASA/JPL-Caltech

And Triton's climate is dynamic and changing, with a steady flow of organic material, likely nitrogen, snowing onto

the surface.

"Triton has always been one of the most exciting and intriguing bodies in the solar system," said Louise Prockter,

director of the Lunar and Planetary Institute/Universities Space Research Association in Houston. As principal

investigator, she would lead the proposed Trident mission, and NASA's Jet Propulsion Laboratory in Southern

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California would manage it. "I've always loved the Voyager 2 images and their tantalizing glimpses of this bizarre,

crazy moon that no one understands," Prockter added.

A Three-Pronged Approach

Those mysterious plumes Voyager 2 spotted are especially intriguing. Plumes seen on Saturn's moon Enceladus,

and possibly present on Jupiter's moon Europa, are thought to be caused by water from the interior being forced

through thick, icy crusts. If an ocean is the source of the plumes on Triton (which lies much farther out in the solar

system than Europa and Enceladus), the discovery would give scientists new information about how interior oceans

form. Unlike other known ocean worlds, Triton's potential ocean likely developed after it was captured by Neptune's

gravity.

It would also expand scientists' understanding of where we might find water. Figuring out what factors lead to a

solar system body having the necessary ingredients to be habitable, which include water, is one Trident's three

major goals. The spacecraft would carry an instrument to probe the moon's magnetic field to determine if an ocean

lies inside, while other instruments would investigate the intense ionosphere, organic-rich atmosphere and bizarre

surface features.

A second goal is to explore vast, unseen lands. Triton offers the largest unexplored solid surface in the solar system

this side of the Kuiper Belt. Most of what we know of the moon came from Voyager 2 data, but we've only seen

40% of the moon's surface. Trident would map most of the remainder.

And Trident would use its full-frame imaging camera to capture the same plume-rich area Voyager 2 imaged — in

full "Neptune-shine," when the Sun's reflected light illuminates the dark side of Triton. That way scientists could

observe changes since the last visit and learn more about just how active Triton is.

Trident's third major goal is to understand how that mysterious surface keeps renewing itself. The surface is

remarkably young, geologically speaking (possibly only 10 million years old in a 4.6-billion-year-old solar system)

and has almost no visible craters. There's also the question of why it looks so different from other icy moons, and

features unusual landforms like dimpled "cantaloupe terrains" and protruding "walled plains." The answers could

shed light on how landscapes develop on other icy bodies.

"Triton is weird, but yet relevantly weird, because of the science we can do there," said Karl Mitchell Trident project

scientist at JPL. "We know the surface has all these features we've never seen before, which motivates us to want

to know 'How does this world work?'

"As we said to NASA in our mission proposal, Triton isn't just a key to solar system science — it's a whole keyring: a

captured Kuiper Belt object that evolved, a potential ocean world with active plumes, an energetic ionosphere and a

young, unique surface."

The proposed launch date in October 2025 (with a backup in October 2026) would take advantage of a once-in-a-

13-year window, when Earth is properly aligned with Jupiter. The spacecraft would use the gravitational pull of

Jupiter as a slingshot straight to Triton for an extended 13-day encounter in 2038.

"The mission designers and navigators are so good at this," said JPL's William Frazier, project systems engineer of

Trident. "After 13 years of flying through the solar system, we can confidently skim the upper edge of Triton's

atmosphere — which is pretty mind-boggling."

And it may seem that time moves slowly in the outer reaches of the solar system, where Neptune's years are long.

Ironically for Triton, the long timeline presents limitations. If Trident arrives before 2040, the team could perform its

test of what's powering the plume activity. Any later, and the Sun moves too far north … for the next hundred

years.

Read more information on Discovery Mission proposals selected to develop concept studies here.

Source: NASA Return to Contents

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2. X-Rays from a Newborn Star Hint at Our Sun's Earliest Days

Credits: X-ray: NASA/CXC/Aix-Marseille University/N. Grosso et al.; Illustration: NASA/CXC/M. Weiss

By detecting an X-ray flare from a very young star using NASA's Chandra X-ray Observatory, researchers have reset

the timeline for when stars like the Sun start blasting high-energy radiation into space. This is significant because it

may help answer some questions about our Sun's earliest days as well as some about the Solar System today.

This artist's illustration depicts the object where astronomers discovered the X-ray flare. HOPS 383 is called a young

"protostar" because it is in the earliest phase of stellar evolution that occurs right after a large cloud of gas and dust

has started to collapse. Once it has matured HOPS 383, which is located about 1,400 light years from Earth, will

have a mass about half that of the Sun.

The illustration shows HOPS 383 surrounded by a donut-shaped cocoon of material (dark brown) — containing

about half of the protostar's mass — that is falling in towards the central star. Much of the light from the infant star

in HOPS 383 is unable to pierce through this cocoon, but X-rays from the flare (blue) are powerful enough to do

so. Infrared light emitted by HOPS 383 is scattered off the inside of the cocoon (white and yellow). A version of the

illustration with a region of the cocoon cut out shows the bright X-ray flare from HOPS 383 and a disk of material

falling towards the protostar.

Chandra observations in December 2017 revealed the X-ray flare, which lasted for about 3 hours and 20 minutes.

The flare is shown as a continuous loop in the inset box of the illustration. The rapid increase and slow decrease in

the amount of X-rays is similar to the behavior of X-ray flares from young stars more evolved than HOPS 383. No X-

rays were detected from the protostar outside this flaring period, implying that during these times HOPS 383 was at

least ten times fainter, on average, than the flare at its maximum. It is also 2,000 times more powerful than the

brightest X-ray flare observed from the Sun, a middle-aged star of relatively low mass.

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As material from the cocoon falls inward toward the disk, there is also an exodus of gas and dust. This "outflow"

removes angular momentum from the system, allowing material to fall from the disk onto the growing young

protostar. Astronomers have seen such an outflow from HOPS 383 and think powerful X-ray flare like the one

observed by Chandra could strip electrons from atoms at the base of it. This may be important for driving the

outflow by magnetic forces.

Credits: NASA/CXC/M. Weiss

As material from the cocoon falls inward toward the disk, there is also an exodus of gas and dust. This "outflow"

removes angular momentum from the system, allowing material to fall from the disk onto the growing young

protostar. Astronomers have seen such an outflow from HOPS 383 and think powerful X-ray flare like the one

observed by Chandra could strip electrons from atoms at the base of it. This may be important for driving the

outflow by magnetic forces.

Furthermore, when the star erupted in X-rays, it would have also likely driven energetic flows of particles that

collided with dust grains located at the inner edge of the disk of material swirling around the protostar. Assuming

something similar happened in our Sun, the nuclear reactions caused by this collision could explain unusual

abundances of elements in certain types of meteorites found on Earth.

No other flares from HOPS 383 were detected over the course of three Chandra observations with a total exposure

of just under a day. Astronomers will need longer X-ray observations to determine how frequent such flares are

during this very early phase of development for stars like our Sun.

A paper describing these results appeared in the journal of Astronomy & Astrophysics and is available online

at https://arxiv.org/abs/2006.02676. The authors of the paper are Nicolas Grosso (Astrophysics Laboratory of

Marseille at Aix-Marseille University in France), Kenji Hamaguchi (Center for Research and Exploration in Space

Science & Technology and NASA's Goddard Space Flight Center in Greenbelt, MD), David Principe (Massachusetts

Institute of Technology), and Joel Kastner (Rochester Institute of Technology).

Source: NASA Return to Contents

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3. Supergiant Atmosphere of Antares Revealed by Radio Telescopes

Artist impression of the atmosphere of Antares. As seen with the naked eye (up until the photosphere),

Antares is around 700 times larger than our sun, big enough to fill the solar system beyond the orbit of Mars

(Solar System scale shown for comparison). But ALMA and VLA showed that its atmosphere, including the

lower and upper chromosphere and wind zones, reaches out 12 times farther than that. Credit:

NRAO/AUI/NSF, S. Dagnello

An international team of astronomers has created the most detailed map yet of the atmosphere of the red

supergiant star Antares. The unprecedented sensitivity and resolution of both the Atacama Large

Millimeter/submillimeter Array (ALMA) and the National Science Foundation’s Karl G. Jansky Very Large Array (VLA)

revealed the size and temperature of Antares’ atmosphere from just above the star’s surface, throughout its

chromosphere, and all the way out to the wind region.

Red supergiant stars, like Antares and its more well-known cousin Betelgeuse, are huge, relatively cold stars at the

end of their lifetime. They are on their way to run out of fuel, collapse, and become supernovae. Through their vast

stellar winds, they launch heavy elements into space, thereby playing an important role in providing the essential

building blocks for life in the universe. But it is a mystery how these enormous winds are launched. A detailed study

of the atmosphere of Antares, the closest supergiant star to Earth, provides a crucial step towards an answer.

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The ALMA and VLA map of Antares is the most detailed radio map yet of any star, other than the Sun. ALMA

observed Antares close to its surface (its optical photosphere) in shorter wavelengths, and the longer wavelengths

observed by the VLA revealed the star’s atmosphere further out. As seen in visible light, Antares’ diameter is

approximately 700 times larger than the Sun. But when ALMA and the VLA revealed its atmosphere in radio light,

the supergiant turned out to be even more gigantic.

“The size of a star can vary dramatically depending on what wavelength of light it is observed with,” explained

Eamon O’Gorman of the Dublin Institute for Advanced Studies in Ireland and lead author of the study published in

the June 16 edition of the journal Astronomy & Astrophysics. “The longer wavelengths of the VLA revealed the

supergiant’s atmosphere out to nearly 12 times the star’s radius.”

The radio telescopes measured the temperature of most of the gas and plasma in Antares’ atmosphere. Most

noticeable was the temperature in the chromosphere. This is the region above the star’s surface that is heated up

by magnetic fields and shock waves created by the vigorous roiling convection at the stellar surface – much like the

bubbling motion in a pot of boiling water. Not much is known about chromospheres, and this is the first time that

this region has been detected in radio waves.

Thanks to ALMA and the VLA, the scientists discovered that the star’s chromosphere extends out to 2.5 times the

star’s radius (our Sun’s chromosphere is only 1/200th of its radius). They also found that the temperature of the

chromosphere is lower than previous optical and ultraviolet observations have suggested. The temperature peaks at

3,500 degrees Celsius (6,400 degrees Fahrenheit), after which it gradually decreases. As a comparison, the Sun’s

chromosphere reaches temperatures of almost 20,000 degrees Celsius.

“We found that the chromosphere is ‘lukewarm’ rather than hot, in stellar temperatures,” said O’Gorman. “The

difference can be explained because our radio measurements are a sensitive thermometer for most of the gas and

plasma in the star’s atmosphere, whereas past optical and ultraviolet observations were only sensitive to very hot

gas and plasma.”

“We think that red supergiant stars, such as Antares and Betelgeuse, have an inhomogeneous atmosphere,” said

co-author Keiichi Ohnaka of the Universidad Católica del Norte in Chile who previously observed Antares’

atmosphere in infrared light. “Imagine that their atmospheres are a painting made out of many dots of different

colors, representing different temperatures. Most of the painting contains dots of the lukewarm gas that radio

telescopes can see, but there are also cold dots that only infrared telescopes can see, and hot dots that UV

telescopes see. At the moment we can’t observe these dots individually, but we want to try that in future studies.”

In the ALMA and VLA data, astronomers for the first time saw a clear distinction between the chromosphere and the

region where winds start to form. In the VLA image, a huge wind is visible, ejected from Antares and lit up by its

smaller but hotter companion star Antares B.

“When I was a student, I dreamt of having data like this,” said co-author Graham Harper of the University of

Colorado, Boulder. “Knowing the actual sizes and temperatures of the atmospheric zones gives us a clue of how

these huge winds start to form and how much mass is being ejected.”

“Our innate understanding of the night sky is that stars are just points of light. The fact we can map the

atmospheres of these supergiant stars in detail, is a true testament to technological advances in interferometry.

These tour de force observations bring the universe close, right into our own backyard,” said Chris Carilli of the

National Radio Astronomy Observatory, who was involved in the first observations of Betelgeuse at multiple radio

wavelengths with the VLA in 1998.

This research was presented in a paper titled “ALMA and VLA reveal the lukewarm chromospheres of the nearby red

supergiants Antares and Betelgeuse,” by E. O’Gorman et al., appearing in the journal Astronomy & Astrophysics.

www.aanda.org/10.1051/0004-6361/202037756

Source: National Radio Astronomy Observatory Return to Contents

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The Night Sky

Look left or lower left of Altair, by hardly more than one fist, for the compact little constellation Delphinus,

the Dolphin.

And by that time, look for Jupiter and Saturn very low three fists to Altair's lower right.

FRIDAY, JUNE 26

Every morning now, Venus is getting a little higher and easier to spot in the east-northeast as dawn

brightens.

SATURDAY, JUNE 27

First-quarter Moon tonight and tomorrow. (The Moon is exactly first-quarter at 4:16 a.m. Sunday morning

EDT.) On Saturday evening for North America, the Moon shines in the hind feet of the Leo stick figure,

about 8° under Leo's 2nd-magnitude tail-tip star, Denebola.

Denebola forms an almost perfectly equilateral triangle with brighter Spica off to its left and Arcturus,

brighter still, above them. All three sides of the triangle are close to 35° long (35.3°, 35.1°, and 32.8°).

This has been called the Spring Triangle, a name that certainly fits. Let's see if we can get it to stick.

Source: Sky and Telescope Return to Contents

TUESDAY, JUNE 23

The central stars of the constellation Lyra, forming a

small triangle and parallelogram, dangle to the lower

right from bright Vega high in the east. The two

brightest stars of the pattern, after Vega, are the two

forming the bottom of the parallelogram: Beta and

Gamma Lyrae, or Sheliak and Sulafat. They're currently

lined up vertically. Beta is the one on top.

Beta Lyrae is an eclipsing binary star. Compare it to

Gamma whenever you look up at Lyra. Normally Beta is

only a trace dimmer than Gamma. Sooner or later,

you'll probably catch Beta when it is definitely fainter

than usual.

WEDNESDAY, JUNE 24

Look left of the Moon for Regulus in late twilight, as

shown at right.

THURSDAY, JUNE 25

Now spot Regulus to the Moon's lower right, as shown

at right.

As evening grows late, even the lowest star of the big

Summer Triangle shines fairly high in the east-

southeast. That's Altair, a good three or four fists at

arm's length below or lower right of Vega.

The thickening crescent moves past Regulus between Wednesday and Thursday evenings for

North America.

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ISS Sighting Opportunities (from Denver)

Date Visible Max Height Appears Disappears

Fri Jun 26, 4:37 AM 4 min 25° 10° above S 18° above E

Sighting information for other cities can be found at NASA’s Satellite Sighting Information

NASA-TV Highlights (all times Eastern Time Zone)

Regularly Scheduled Programming

NASA TV Schedule for Week of June 22

Live Programming

June 24, Wednesday

1:10 p.m. – International Space Station Expedition 63 in-flight event with CBS’ "Late Late Show" with

James Corden and NPR’s Morning Edition and astronauts Bob Behnken and Doug Hurley of NASA (All

Channels)

2 p.m. – International Space Station Expedition 63 spacewalk preview briefing (All Channels)

June 25, Thursday

3 p.m. - NASA Science Live: Science in the Time of Coronavirus (All Channels)

June 26, Friday

6 a.m. – International Space Station Expedition 63 U.S. spacewalk #65 coverage. Spacewalk is scheduled

to begin at 7:35 a.m. EDT with Cassidy and Behnken and expected to last up to 7 hours (All Channels)

Watch NASA TV online by going to the NASA website. Return to Contents

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Space Calendar

Jun 23 - Webinar: Women's Health in Space

Jun 23 - Webinar: Staking Your Claim to the Trillion-Dollar Space Economy

Jun 23 - Online: Teaching Space With NASA -Engineering the Perseverance Mars Rover

Jun 23 - Online Seminar: The Energy of Dark Matter Haloes - A New Guideline to Model Virialized Structures

Jun 23 - Webinar: Plant Growth Research and Technologies

Jun 23-24 - Conference: Made for Space 2020, Coventry, United Kingdom

Jun 23-24 - Virtual Workshop: Monitoring Anthropogenic CO2 Emissions with Copernicus

Jun 23-25 - Virtual Workshop: The Next-Generation Ground-Based Planetary Radar

Jun 24 - Starlink 9 (60)/BlackSky Global 5 & 6 Falcon 9 Launch

Jun 24 - Aten Asteroid 441987 (2010 NY65) Near-Earth Flyby (0.025 AU)

Jun 24 - Webinar: The Hunt for Dark Matter at the Large Hadron Collider

Jun 25 - Apollo Asteroid 2017 FW128 Near-Earth Flyby (0.008 AU)

Jun 25 - Apollo Asteroid 2020 MA Near-Earth Flyby (0.014 AU)

Jun 25 - Asteroid 90022 Apache Point Closest Approach To Earth (1.576 AU)

Jun 25 - Space Tourism Conference, Los Angeles, California

Jun 25 - Webinar: The How, When, and Why of Using EO Data in Climate Resilience Decision-making

Jun 25 - Webinar: Microgravity Services and Applications

Jun 25 - Live Chat: Facing the Challenge

Jun 25-26 - International Conference on Astronomical Computing and Measurement (ICACM 2020), Istanbul, Turkey

Jun 25-26 - International Conference on Physical Cosmology and Dark Matter (ICPCDM 2020), Paris, France

Jun 25-30 - International School of Physics: Foundations of Cosmic Ray Astrophysics, Varenna, Lake Como, Italy

Jun 26 - Comet 2P/Encke Perihelion (0.337 AU)

Jun 26 - 9th Virtual Mars Exploration Program Analysis Group (MEPAG) Meeting

Jun 27 - Aten Asteroid 2020 KQ7 Near-Earth Flyby (0.027 AU)

Jun 27 - Apollo Asteroid 2020 MK Near-Earth Flyby (0.031 AU)

Jun 27 - Asteroid 2575 Bulgaria Closest Approach To Earth (0.976 AU)

Jun 28- Apstar 6D CZ-3B/G2 Launch

Jun 28 - Apollo Asteroid 2020 ME1 Near-Earth Flyby (0.005 AU)

Source: JPL Space Calendar Return to Contents

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Food for Thought

New Distance Measurements Bolster Challenge to Basic Model of

Universe

Artist's conception illustrating a disk of water-bearing gas orbiting the supermassive black hole at the core of a distant

galaxy. By observing maser emission from such disks, astronomers can use geometry to measure the distance to the

galaxies, a key requirement for calculating the Hubble Constant. Credit: Sophia Dagnello, NRAO/AUI/NSF

A new set of precision distance measurements made with an international collection of radio telescopes have

greatly increased the likelihood that theorists need to revise the “standard model” that describes the

fundamental nature of the Universe.

The new distance measurements allowed astronomers to refine their calculation of the Hubble Constant, the

expansion rate of the Universe, a value important for testing the theoretical model describing the composition

and evolution of the Universe. The problem is that the new measurements exacerbate a discrepancy between

previously measured values of the Hubble Constant and the value predicted by the model when applied to

measurements of the cosmic microwave background made by the Planck satellite.

“We find that galaxies are nearer than predicted by the standard model of cosmology, corroborating a problem

identified in other types of distance measurements. There has been debate over whether this problem lies in

the model itself or in the measurements used to test it. Our work uses a distance measurement technique

completely independent of all others, and we reinforce the disparity between measured and predicted values.

It is likely that the basic cosmological model involved in the predictions is the problem,” said James Braatz, of

the National Radio Astronomy Observatory (NRAO).

Braatz leads the Megamaser Cosmology Project, an international effort to measure the Hubble Constant by

finding galaxies with specific properties that lend themselves to yielding precise geometric distances. The

project has used the National Science Foundation’s Very Long Baseline Array (VLBA), Karl G. Jansky Very

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Large Array (VLA), and Robert C. Byrd Green Bank Telescope (GBT), along with the Effelsberg telescope in

Germany. The team reported their latest results in the Astrophysical Journal Letters.

Edwin Hubble, after whom the orbiting Hubble Space Telescope is named, first calculated the expansion rate

of the universe (the Hubble Constant) in 1929 by measuring the distances to galaxies and their recession

speeds. The more distant a galaxy is, the greater its recession speed from Earth. Today, the Hubble Constant

remains a fundamental property of observational cosmology and a focus of many modern studies.

Measuring recession speeds of galaxies is relatively straightforward. Determining cosmic distances, however,

has been a difficult task for astronomers. For objects in our own Milky Way Galaxy, astronomers can get

distances by measuring the apparent shift in the object’s position when viewed from opposite sides of Earth’s

orbit around the Sun, an effect called parallax. The first such measurement of a star’s parallax distance came

in 1838.

Beyond our own Galaxy, parallaxes are too small to measure, so astronomers have relied on objects called

“standard candles,” so named because their intrinsic brightness is presumed to be known. The distance to an

object of known brightness can be calculated based on how dim the object appears from Earth. These

standard candles include a class of stars called Cepheid variables and a specific type of stellar explosion called

a Type Ia supernova.

Another method of estimating the expansion rate involves observing distant quasars whose light is bent by the

gravitational effect of a foreground galaxy into multiple images. When the quasar varies in brightness, the

change appears in the different images at different times. Measuring this time difference, along with

calculations of the geometry of the light-bending, yields an estimate of the expansion rate.

Determinations of the Hubble Constant based on the standard candles and the gravitationally-lensed quasars

have produced figures of 73-74 kilometers per second (the speed) per megaparsec (distance in units favored

by astronomers).

However, predictions of the Hubble Constant from the standard cosmological model when applied to

measurements of the cosmic microwave background (CMB) — the leftover radiation from the Big Bang —

produce a value of 67.4, a significant and troubling difference. This difference, which astronomers say is

beyond the experimental errors in the observations, has serious implications for the standard model.

The model is called Lambda Cold Dark Matter, or Lambda CDM, where “Lambda” refers to Einstein’s

cosmological constant and is a representation of dark energy. The model divides the composition of the

Universe mainly between ordinary matter, dark matter, and dark energy, and describes how the Universe has

evolved since the Big Bang.

The Megamaser Cosmology Project focuses on galaxies with disks of water-bearing molecular gas orbiting

supermassive black holes at the galaxies’ centers. If the orbiting disk is seen nearly edge-on from Earth, bright

spots of radio emission, called masers — radio analogs to visible-light lasers — can be used to determine both

the physical size of the disk and its angular extent, and therefore, through geometry, its distance. The

project’s team uses the worldwide collection of radio telescopes to make the precision measurements required

for this technique.

In their latest work, the team refined their distance measurements to four galaxies, at distances ranging from

168 million light-years to 431 million light-years. Combined with previous distance measurements of two other

galaxies, their calculations produced a value for the Hubble Constant of 73.9 kilometers per second per

megaparsec.

“Testing the standard model of cosmology is a really challenging problem that requires the best-ever

measurements of the Hubble Constant. The discrepancy between the predicted and measured values of the

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Hubble Constant points to one of the most fundamental problems in all of physics, so we would like to have

multiple, independent measurements that corroborate the problem and test the model. Our method is

geometric, and completely independent of all others, and it reinforces the discrepancy,” said Dom Pesce, a

researcher at the Center for Astrophysics | Harvard and Smithsonian, and lead author on the latest paper.

“The maser method of measuring the expansion rate of the universe is elegant, and, unlike the others, based

on geometry. By measuring extremely precise positions and dynamics of maser spots in the accretion disk

surrounding a distant black hole, we can determine the distance to the host galaxies and then the expansion

rate. Our result from this unique technique strengthens the case for a key problem in observational

cosmology.” said Mark Reid of the Center for Astrophysics | Harvard and Smithsonian, and a member of the

Megamaser Cosmology Project team.

“Our measurement of the Hubble Constant is very close to other recent measurements, and statistically very

different from the predictions based on the CMB and the standard cosmological model. All indications are that

the standard model needs revision,” said Braatz.

Astronomers have various ways to adjust the model to resolve the discrepancy. Some of these include

changing presumptions about the nature of dark energy, moving away from Einstein’s cosmological constant.

Others look at fundamental changes in particle physics, such as changing the numbers or types of neutrinos or

the possibilities of interactions among them. There are other possibilities, even more exotic, and at the

moment scientists have no clear evidence for discriminating among them.

“This is a classic case of the interplay between observation and theory. The Lambda CDM model has worked

quite well for years, but now observations clearly are pointing to a problem that needs to be solved, and it

appears the problem lies with the model,” Pesce said.

“The Megamaser Cosmology Project. XIII. Combined Hubble Constant Constraints,” D. W. Pesce, 2020 Feb.

26, Astrophysical Journal Letters.

Clouds linger at twilight over the Karl G. Jansky Very Large Array in its most compact configuration. Credit:

NRAO/AUI/NSF

Source: National Radio Astronomy Observatory Return to Contents

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Space Image of the Week

Comet PanSTARRs and the Galaxies Image Credit & Copyright: Dan Bartlett

Explanation: Comet PanSTARRs, C/2017 T2, shared this stunning telescopic field of view with galaxies M81 and M82 on May 22/23. Of course, the galaxies were some 12 million light-years distant and the comet about 14 light-minutes away, seen in planet Earth's sky toward the Big Dipper. A new visitor from the Oort Cloud, this Comet PanSTARRs was discovered in 2017 by the PanSTARRs survey telescope when the comet was over 1 light-hour from the Sun, almost as distant as the orbit of Saturn. With a beautiful coma and dust tail, this comet has been a solid northern hemisphere performer for telescope wielding comet watchers this May, following its closest approach to the Sun on May 4. In this deep image from dark California skies the outbound comet even seems to develop a short anti-tail as it leaves the inner Solar System.

Source: NASA APOD Return to Contents