coming events volume 45 number 08 monthly meeting...
TRANSCRIPT
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COMING EVENTS Monthly Meeting
SUNDAY AUGUST 25, 7:00 PM
SEPTEMBER 29, 7:00 PM
PUBLIC OBSERVING SUNDAY
AUGUST 25, ~9:00 PM SEPTEMBER 29, 8:15 PM
BAKER WETLANDS DISCOVERY CENTER
Regional Event NASA EYES/KANSAS MINDS
Sat. Oct. 12, KU - ISB
President Rick Heschmeyer
[email protected] ALCOR
William Winkler [email protected]
NSN Coordinator Howard Edin
Report from the Officers
Summer observing is over, at least downtown, and the new school year is almost upon us. With the latter comes our re-turn to regular monthly meet-ings and public observing at the Baker Wetlands Discovery Center. Our first meeting is, as usual, the last Sunday of the month, August 25, at 7 PM, followed by observing after about 9:00 PM, weather per-mitting Since this first meeting
will help set the agenda for the remainder of the year, please come by for some con-versation and refreshments. Of particular importance will be a discussion of the NASA Eyes, Kansas Minds conference (see below), where AAL and a number of other groups will have public displays to help promote the event and astronomy in general. The two final public events for the summer went well. Bill Winkler reports that the post-Band Concert Observing on July 10 included 3 scopes, a 17-inch Dob, 8-inch SCT, and a 4-inch refractor used by ~ 30 people to view the Moon, Jupi-
ter and, toward the end, Saturn. For viewing from the Parking Garage south of the library on the previous night, there were about six telescopes of several types, in-cluding the 17-inch Dobsonian, on the brightly lit rooftop. As with the downtown Band
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Volume 45 Number 08 August 2019
INSIDE THIS ISSUE
Officers (continued) 2
NASAEYES/KANSAS MINDS 2
Spinning Black Holes 3
NASA Night Sky Notes 4
NASA NSN (continued) 5
Expansion Rate (continued) 5
OOTW Planet (continued) 5
Expansion Rate Controversy 6
Out-of-this-World Planet 7
Chandra 20-Yr Anniversary 8
Chandra (continued) 9
Death by Dark Matter? 10
August Scene 11
LPL Photos 11
August Skies 12
Of Local Interest
NASA EYES/KANSAS MINDS
There are a great many anniversaries this year, the most famous being the moon landing. However, this year is also the 60th anniversary of the founding of NASA. As part of the national celebration, on October 12, 2019, the University of Kansas Phys-ics and Astronomy Department will host a one-day conference, NASA Eyes, Kansas Minds. It will commemorate the use of NASA space telescopes by Kansans and laud the scientific achievements of Kansas scientists made possible by those mis-sions. The conference is open to all and will feature talks and posters by scientists across the state as well as four keynote addresses aimed at the general public (see the updated schedule on the website, http://nasaeyes.ku.edu/, listing all keynote talks and exhibitors.) As part of our poster sessions, we will have hands-on exhibits aimed at undergraduate and high school students and teachers. Our conference mission is to promote scientific interaction and public engagement across the state and extol the importance of continued support for NASA missions to boost the scientific and economic welfare of Kansas. Please register to attend at: http://nasaeyes.ku.edu/. Registration is free (and lunch is provided), but we need an accurate head count. You can also submit an abstract to be considered for a poster or brief talk (~10min). The deadline to submit an abstract is August 31st. Submissions can be made on the registration page on our web-
site. The deadline to register to attend the conference is September 30th.
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About the Astronomy Associates of Lawrence
The club is open to all people interested in sharing their love for astronomy. Beginning in Fall 2016, monthly meetings are typical-ly on the last Sunday of each month and often feature guest speakers, presentations by club members, and a chance to ex-
change amateur astronomy tips. These meetings and the public observing sessions that follow are scheduled at the Baker Wet-lands Discovery Center, south of Lawrence. All events and meetings are free and open to the public. Periodic star parties are
scheduled as well. For more information, please contact the club officers: President Rick Heschmeyer at
[email protected]; AlCor William Winkler at [email protected]; NSN Coordinator Howard Edin at how-
[email protected], or faculty advisor Prof. Bruce Twarog at [email protected]. Because of the flexibility of the schedule due to holidays and alternate events, it is always best to check the Web site for the exact Sundays when events are scheduled. The
information about AAL can be found at http://www.physics.ku.edu/AAL/
Copies of the Celestial Mechanic can also be found on the web at http://www.physics.ku.edu/AAL/newsletter
Concert observing, only Jupiter and the Moon were viewable, as well as Saturn, once again briefly low on horizon at 10 PM. Over 100 people attended the two-hour event. Many thanks to LPL for its cooperation and support. (See photo on pg. 11).
Any suggestions for improving the club or the newsletter are always welcome.
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A Stellar Welcome to new club member:
FLAVIO CURELLA
Hope to see you at the next club meeting on August 25.
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X-rays Spot Spinning Black Holes Across Cosmic Sea
Like whirlpools in the ocean, spinning black holes in space create a swirling torrent around them. However, black holes do not create eddies of wind or water. Rather, they generate disks of gas and dust heated to hundreds of millions of degrees that glow in X-ray light.
Using data from NASA's Chandra X-ray Observatory and chance alignments across billions of light years, astrono-mers have deployed a new technique to measure the spin of five supermassive black holes. The matter in one of these cosmic vortices is swirling around its black hole at greater than about 70% of the speed of light.
The astronomers took advantage of a natural phenom-enon called a gravitational lens. With just the right alignment, the bending of space-time by a massive object, such as a large galaxy, can magnify and pro-duce multiple images of a distant object, as predicted by Einstein.
In this latest research, astronomers used Chandra and gravitational lensing to study five quasars, each con-sisting of a supermassive black hole rapidly consum-ing matter from a surrounding accretion disk. Gravita-tional lensing of the light from each of these quasars by an intervening galaxy has created multiple images of each quasar, as shown by these Chandra images of four of the targets. The sharp imaging ability of Chan-dra is needed to separate the multiple, lensed images of each quasar.
The key advance made by researchers in this study was that they took advantage of "microlensing," where individual stars in the intervening, lensing galaxy pro-vided additional magnification of the light from the quasar. A higher magnification means a smaller region is producing the X-ray emission.
The researchers then used the property that a spin-ning black hole is dragging space around with it and allows matter to orbit closer to the black hole than is possible for a non-spinning black hole. Therefore, a smaller emitting region corresponding to a tight orbit generally implies a more rapidly spinning black hole. The authors concluded from their microlensing analysis that the X-rays come from such a small region that the black holes must be spinning rapidly.
The results showed that one of the black holes, in the lensed quasar called the "Einstein Cross," (labeled Q2237 in the image above) is spinning at, or almost at, the maximum rate possible. This corresponds to the event horizon, the black hole's point of no return, spinning at the speed of light, which is about 670 million miles per hour. Four other black holes in the sample are spinning, on average, at about half this maximum rate.
For the Einstein Cross the X-ray emission is from a part of the disk that is less than about 2.5 times the size of the event horizon, and for the other 4 quasars the X-rays come from a region four to five times the size of the event horizon.
How can these black holes spin so quickly? The researchers think that these supermassive black holes likely grew by accumulating most of their material over billions of years from an accretion disk spinning with a similar orienta-tion and direction of spin, rather than from random directions. Like a merry-go-round that keeps getting pushed in the same direction, the black holes kept picking up speed.
The X-rays detected by Chandra are produced when the accretion disk surrounding the black hole creates a multi-million-degree cloud, or corona above the disk near the black hole. X-rays from this corona reflect off the inner edge of the accretion disk, and the strong gravitational forces near the black hole distort the reflected X-ray spectrum, that is, the amount of X-rays seen at different energies. The large distortions seen in the X-ray spectra of the qua-sars studied here imply that the inner edge of the disk must be close to the black holes, giving further evidence that they must be spinning rapidly.
The quasars are located at distances ranging from 9.8 billion to 10.9 billion light years from Earth, and the black holes have masses between 160 and 500 million times that of the sun. These observations were the longest ever made with Chandra of gravitationally lensed quasars, with total exposure times ranging between 1.7 and 5.4 days.
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Chill Out: Spot an Ice Giant in August
By David Prosper
Is the summer heat getting to you? Cool off overnight while spotting one of the solar system’s ice giants: Neptune! It’s the perfect way to commemorate the 30th anniversary of Voyager 2’s flyby.
Neptune is too dim to see with your unaided eye so you’ll need a telescope to find it. Neptune is at opposition in Sep-tember, but its brightness and apparent size won’t change dramatically as it’s so distant; the planet is usually just un-der 8th magnitude and 4.5 billion kilometers away. You can see Neptune with binoculars but a telescope is recom-mended if you want to discern its disc; the distant world reveals a very small but discernible disc at high magnifica-tion. Neptune currently appears in Aquarius, a constellation lacking in bright stars, which adds difficulty to pinpointing its exact location. Fortunately, the Moon travels past Neptune the night of August 16th, passing less than six degrees apart (or about 12 Moon widths) at their closest. If the Moon’s glare overwhelms Neptune’s dim light, you can still use the its location that evening to mark the general area to search on a darker night. Another Neptune-spotting tip: Draw an imaginary line from bright southern star Fomal-haut up to the Great Square of Pegasus, then mark a point roughly in the middle and search there, in the eastern edge of Aquarius. If you spot a blue-ish star, swap your tele-scope’s eyepiece to zoom in as much as possible. Is the suspect blue “star” now a tiny disc, while the surrounding stars remain points of white light? You’ve found Neptune!
Neptune and Uranus are ice giant planets. These worlds are larger than terrestrial worlds like Earth but smaller than gas giants like Jupiter. Nep-tune’s atmosphere contains hydrogen and helium like a gas giant, but also methane, which gives it a striking blue color. The “ice” in “ice giant” refers to the mix of ammonia, methane, and water that makes up most of Neptune’s mass, located in the planet’s large, dense, hot mantle. This mantle surrounds an Earth-size rocky core. Neptune possesses a faint ring system and 13 confirmed moons. NASA’s Voyager 2 mission made a very close flyby on August 25, 1989. It revealed a dynamic, stormy world streaked by the fastest winds in the solar system, their ferocity fueled by
the planet’s sur-prisingly strong internal heating. Triton, Neptune’s largest moon, was discovered to be geologically active, with cry-ovolcanoes erupting nitrogen gas and dust
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Clockwise from top left: Neptune and the Great Dark Spot traced by white clouds; Neptune’s rings; Triton and its famed icy cantaloupe surface; close of up Tri-ton’s surface, with dark streaks indicating possible cyrovolcano activity. Find more images and science from Voyager 2’s flyby at bit.ly/NeptuneVoyager2 Im-age Credit: NASA/JPL
Finder chart for Neptune. This is a simulated view through 10x50 binoculars (10x magnification). Please note that the sizes of stars in this chart indicate their brightness, not their actual size. Moon image courtesy NASA Scientific Visualization Studio; chart creat-ed with assistance from Stellarium.
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dotting its surface, and a mottled “cantaloupe” terrain made up of hard water ice. Triton is similar to Pluto in size and composition, and orbits Neptune in the opposite direction of the planet’s rotation, unlike every other large moon in the solar system. These clues lead scientists to conclude that this unusual moon is likely a captured Kuiper Belt object. Discover more about Voyager 2, along with all of NASA’s past, present, and future missions, at nasa.gov
This article is distributed by NASA Night Sky Network The Night Sky Network program supports astrono-my clubs across the USA dedicated to astronomy outreach. Visit nightsky.jpl.nasa.org to find local clubs, events, and more!
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How to Measure Expansion
A central challenge in measuring the universe's expansion rate is that it is very difficult to accurately calculate dis-tances to distant objects.
In 2001, Freedman led a team that used distant stars to make a landmark measurement of the Hubble constant. The Hubble Space Telescope Key Project team measured the value using Cepheid variables as distance markers. Their program concluded that the value of the Hubble constant for our universe was 72 km/sec/Mpc.
But more recently, scientists took a very different approach: building a model based on the rippling structure of light left over from the big bang, which is called the Cosmic Microwave Background. The Planck measurements allow scientists to predict how the early universe would likely have evolved into the expansion rate astronomers can measure today. Scientists calculated a value of 67.4 km/sec/Mpc, in significant disagreement with the rate of 74.0 km/sec/Mpc measured with Cepheid stars.
Astronomers have looked for anything that might be causing the mismatch. "Naturally, questions arise as to wheth-er the discrepancy is coming from some aspect that astronomers don't yet understand about the stars we're meas-uring, or whether our cosmological model of the universe is still incomplete," Freedman said. "Or maybe both need to be improved upon."
Freedman's team sought to check their results by establishing a new and entirely independent path to the Hubble constant using an entirely different kind of star.
Certain stars end their lives as a very luminous kind of star called a red giant, a stage of evolution that our own Sun will experience billions of years from now. At a certain point, the star undergoes a catastrophic event called a heli-um flash, in which the temperature rises to about 100 million degrees and the structure of the star is rearranged, which ultimately dramatically decreases its luminosity. Astronomers can measure the apparent brightness of the red giant stars at this stage in different galaxies, and they can use this as a way to tell their distance. The Hubble constant is calculated by comparing distance values to the apparent recessional velocity of the target galaxies — that is, how fast galaxies seem to be moving away. The team's calculations give a Hubble constant of 69.8 km/sec/Mpc — straddling the values derived by the Planck and Riess teams.
"Our initial thought was that if there's a problem to be resolved between the Cepheids and the Cosmic Microwave Background, then the red giant method can be the tie-breaker," said Freedman.
But the results do not appear to strongly favor one answer over the other say the researchers, although they align more closely with the Planck results. NASA's upcoming mission, the Wide Field Infrared Survey Telescope (WFIRST), scheduled to launch in the mid-2020s, will enable astronomers to better explore the value of the Hubble constant across cosmic time. WFIRST, with its Hubble-like resolution and 100 times greater view of the sky, will provide a wealth of new Type Ia supernovae, Cepheid variables, and red giant stars to fundamentally improve dis-tance measurements to galaxies near and far.
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hypothesizes that essentially it started out as a dry rock, and rapidly accreted hydrogen from a primordial disk of gas when its star was very young. The disk is called a "protoplanetary disk."
"We're seeing an object that was able to accrete hydrogen from the protoplanetary disk, but didn’t runaway to be-come a hot Jupiter," said Benneke. "This is an intriguing regime."
One explanation is that the disk dissipated before the planet could bulk up further. "The planet got stuck being a sub-Neptune," said Benneke.
NASA's upcoming James Webb Space Telescope will be able to probe even deeper into GJ 3470 b's atmosphere thanks to the Webb's unprecedented sensitivity in the infrared. The new results have already spawned large inter-est by American and Canadian teams developing the instruments on Webb. They will observe the transits and eclipses of GJ 3470 b at light wavelengths where the atmospheric hazes become increasingly transparent.
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Red Giant Stars Used as Milepost Markers
Astronomers have made a new measurement of how fast the universe is expanding, using an entirely different kind of star than previous endeavors. The revised measurement, which comes from NASA's Hubble Space Telescope, falls in the center of a hotly debated question in astrophysics that may lead to a new interpretation of the universe's fundamental properties.
Scientists have known for almost a century that the universe is expanding, meaning the distance between galaxies across the universe is becoming ever more vast every second. But exactly how fast space is stretching, a value
known as the Hubble constant, has re-mained stubbornly elusive.
Now, University of Chicago professor Wendy Freedman and colleagues have a new measurement for the rate of ex-pansion in the modern universe, sug-gesting the space between galaxies is stretching faster than scientists would expect. Freedman's is one of several recent studies that point to a nagging discrepancy between modern expansion measurements and predictions based on the universe as it was more than 13 bil-lion years ago, as measured by the Eu-ropean Space Agency's Planck satellite.
As more research points to a discrepan-cy between predictions and observa-tions, scientists are considering whether they may need to come up with a new model for the underlying physics of the universe in order to explain it.
"The Hubble constant is the cosmologi-cal parameter that sets the absolute scale, size and age of the universe; it is one of the most direct ways we have of quantifying how the universe evolves," said Freedman. "The discrepancy that we saw before has not gone away, but this new evidence suggests that the jury is still out on whether there is an imme-diate and compelling reason to believe that there is something fundamentally flawed in our current model of the uni-verse.”
In a new paper, Freedman and her team announced a new measurement of the Hubble constant using a kind of star known as a red giant. Their new obser-vations, made using Hubble, indicate that the expansion rate for the nearby universe is just under 70 kilometers per second per megaparsec (km/sec/Mpc). One parsec is equivalent to 3.26 light-
years distance.
This measurement is slightly smaller than the value of 74 km/sec/Mpc recently reported by the Hubble SH0ES (Supernovae H0 for the Equation of State) team using Cepheid variables, which are stars that pulse at regular inter-vals that correspond to their peak brightness. This team, led by Adam Riess of the Johns Hopkins University and Space Telescope Science Institute, Baltimore, Maryland, recently reported refining their observations to the highest precision to date for their Cepheid distance measurement technique.
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These galaxies are selected from a Hubble Space Telescope program to measure the expansion rate of the universe, called the Hubble con-stant. The value is calculated by comparing the galaxies' distances to the apparent rate of recession away from Earth (due to the relativistic effects of expanding space). By comparing the apparent brightnesses of the galaxies' red giant stars with nearby red giants, whose distances were measured with other methods, astronomers are able to determine how far away each of the host galaxies are. This is possible because red giants are reliable milepost markers because they all reach the same peak brightness in their late evolution. And, this can be used as a "standard candle" to calculate distance. Hubble's exquisite sharpness and sensitivity allowed for red giants to be found in the stellar halos of the host galaxies.
The red giants were searched for in the halos of the galaxies. The cen-ter row shows Hubble's full field of view. The bottom row zooms even tighter into the Hubble fields. The red giants are identified by yellow circles.
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Mysterious World Is Unlike Anything Found in Our Solar System
Two NASA space telescopes have teamed up to identify, for the first time, the detailed chemical "fingerprint" of a planet between the sizes of Earth and Neptune. No planets like this can be found in our own solar system, but they are common around other stars.
The planet, Gliese 3470 b (also known as GJ 3470 b), may be a cross between Earth and Neptune, with a large rocky core buried under a deep crushing hydrogen and helium atmosphere. Weighing in at 12.6 Earth masses, the planet is more massive than Earth, but less massive than Neptune (which is more than 17 Earth masses).
Many similar worlds have been discovered by NASA's Kepler space telescope, whose mission ended in 2018. In fact, 80% of the planets in our galaxy may fall into this mass range. However, astronomers have never been able to understand the chemical nature of such a planet until now, researchers say.
By inventorying the contents of GJ 3470 b's atmosphere, astronomers are able to uncover clues about the planet's nature and origin. "This is a big discovery from the planet formation per-spective. The planet orbits very close to the star and is far less massive than Jupiter—318 times Earth's mass—but has managed to accrete the primordial hydrogen/helium atmosphere that is largely "unpolluted" by heavier elements," said Björn Benneke of the University of Mon-treal, Canada. "We don't have anything like this in the solar system, and that's what makes it striking."
Astronomers enlisted the combined multi-wavelength capabilities NASA's Hubble and Spitzer space tele-scopes to do a first-of-a-kind study of GJ 3470 b's atmos-phere.
This was accomplished by measuring the absorption of starlight as the planet passed in front of its star (transit) and the loss of reflected light from the planet as it passed behind the star (eclipse). All totaled, the space tele-scopes observed 12 transits and 20 eclipses. The sci-ence of analyzing chemical fingerprints based on light is called "spectroscopy."
"For the first time we have a spectroscopic signature of such a world," said Benneke. But he is at a loss for clas-sification: Should it be called a "super-Earth" or "sub-Neptune?" Or perhaps something else?
Fortuitously, the atmosphere of GJ 3470 b turned out to be mostly clear, with only thin hazes, enabling the scien-tists to probe deep into the atmosphere.
"We expected an atmosphere strongly enriched in heavi-er elements like oxygen and carbon which are forming abundant water vapor and methane gas, similar to what we see on Neptune", said Benneke. "Instead, we found an atmosphere that is so poor in heavy elements that its composition resembles the hydrogen/helium rich compo-sition of the Sun."
Other exoplanets called "hot Jupiters" are thought to form far from their stars, and over time migrate much closer. But this planet seems to have formed just where it is today, says Benneke.
The most plausible explanation, according to Benneke, is that GJ 3470 b was born precariously close to its red dwarf star, which is about half the mass of our Sun. He
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This artist's illustration shows the theoretical internal
structure of the exoplanet GJ 3470 b. It is unlike any
planet found in the Solar System. Weighing in at 12.6
Earth masses the planet is more massive than Earth
but less massive than Neptune. Unlike Neptune, which
is 3 billion miles from the Sun, GJ 3470 b may have
formed very close to its red dwarf star as a dry, rocky
object. It then gravitationally pulled in hydrogen and
helium gas from a circumstellar disk to build up a thick
atmosphere. The disk dissipated many billions of years
ago, and the planet stopped growing. The bottom illus-
tration shows the disk as the system may have looked
long ago. Observations by NASA's Hubble and Spitzer
space telescopes have chemically analyzed the compo-
sition of GJ 3470 b's very clear and deep atmosphere,
yielding clues to the planet's origin. Many planets of this
mass exist in our galaxy.
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NASA's Chandra X-ray Observatory Celebrates Its 20th Anniversary
On July 23, 1999, the Space Shuttle Columbia blasted off from the Kennedy Space Center carrying the Chandra X-ray Observatory. In the two decades that have passed, Chandra's powerful and unique X-ray eyes have contribut-ed to a revolution in our understanding of the cosmos. "In this year of exceptional anniversaries — 50 years after Apollo 11 and 100 years after the solar eclipse that proved Einstein's General Theory of Relativity — we should not lose sight of one more," said Paul Hertz, Director of Astrophysics at NASA. "Chandra was launched 20 years ago, and it continues to deliver amazing science discoveries year after year." To commemorate Chandra's 20th anniver-sary of science operations, NASA has released new images representing the breadth of Chandra's exploration, demonstrating the variety of objects it studies as well as how X-rays complement the data collected in other types of light. From the colossal grandeur of a galaxy cluster to the light from infant stars, these new images are a sam-ple of Chandra's spectacular X-ray vision. Chandra is one of NASA's "Great Observatories" (along with the Hubble Space Telescope, Spitzer Space Telescope, and Compton Gamma Ray Observatory), and has the sharpest vision of any X-ray telescope ever built. It is often used in conjunction with telescopes like Hubble and Spitzer that ob-serve in different parts of the electromagnetic spectrum, and with other high-energy missions like the European Space Agency's XMM-Newton and NASA's NuSTAR. Chandra's discoveries have impacted virtually every aspect of astrophysics. For example, Chandra was involved in a direct proof of dark matter's existence. It has witnessed powerful eruptions from supermassive black holes. Astronomers have also used Chandra to map how the elements essential to life are spread from supernova explosions.
The 20th anniversary images are from left to right:
Top row: Abell 2146: The colossal system Abell 2146 is the result of a collision and merger between two galaxy clusters. Astronomers think that galaxy clusters, the largest structures in the Universe held together by gravity, grow by colliding and merging with one another. Mergers of galaxy clusters are some of the most energetic events since the Big Bang. Chandra has observed many galaxy cluster mergers, giving scientists insight into how these mega-structures that dominate the Universe came to be. In this image of Abell 2146, X-rays from Chandra (purple) show hot gas and optical data from the Hubble Space Telescope shows galaxies and stars. The bullet-shaped feature shows the hot gas from one cluster plowing through the hot gas in the other cluster.
Sagittarius A* (Galactic Center): The central region of our galaxy, the Milky Way, contains an exotic collection of objects, including a supermassive
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black hole weighing about 4 million times the mass of the Sun (called Sagittarius A*), clouds of gas at temperatures of millions of degrees, neutron stars and white dwarf stars tearing material from companion stars and beautiful ten-drils of radio emission. The region around Sagittarius A* is shown in this new composite image with Chandra data (green and blue) combined with radio data (red) from the MeerKAT telescope in South Africa, which will eventually become part of the Square Kilometer Array (SKA).
30 Doradus: At the center of 30 Doradus, one of the largest star-forming regions located close to the Milky Way, thousands of massive stars are blowing off material and producing intense radiation along with powerful winds. Chandra detects gas that has been heated to millions of degrees by these stellar winds and also by supernova explosions that mark the end of some giant stars' lives. These X-rays come from shock fronts, similar to sonic booms produced by super-sonic airplanes, that rumble through the system. This new Chandra image of 30 Doradus, which is nicknamed the "Tarantula Nebula," contains data from several long observations totaling almost 24 days of observing spread out over about 700 days. The colors in this Chandra image are red, green and purple to highlight low, medium and high X-ray energies respectively.
Astronomers used the long set of Chandra observations to discover that one of the bright X-ray sources shows reg-ular variations in its X-ray output, with a period of 155 days. This variation originates from two massive stars orbiting each other, in a double-star system called Melnick 34. Follow-up observations with the European Southern Obser-vatory's Very Large Telescope and the Gemini Observatory, both in Chile, measured the change in velocities of both stars during their orbit, leading to mass estimates of 139 and 127 times the mass of the sun. This makes Melnick 34 the most massive binary known, as reported in a paper published earlier this year, led by Katie Tehrani of the University of Sheffield in the UK. Within about two or three million years, both stars should implode to form black holes. If the binary survives these violent events, the black holes might eventually merge to produce a burst of gravitational waves. The X-rays likely originate from shock waves generated by the collision of material blowing away from the surfaces of both stars, making Melnick 34 a "colliding-wind binary".
Bottom row:
Cygnus OB2: Stars come in different sizes and masses. Our Sun is an average-sized star that will have a lifespan of some 10 billion years. More massive stars, like those found in Cygnus OB2, only last a few million years. During their life-times, they blast large amounts of high-energy winds into their surroundings. These violent winds can collide or produce shocks in the gas and dust around the stars, depositing large amounts of energy that produce X-ray emis-sion that Chandra can detect. In this composite image of Cygnus OB2, X-rays from Chandra (red diffuse emission and blue point sources) are shown with optical data from the Isaac Newton Telescope (diffuse emission in light blue) and infrared data from the Spitzer Space Telescope (orange). NGC 604: The nearby galaxy Messier 33 contains a star-forming region called NGC 604 where some 200 hot, young, massive stars reside. The cool dust and warmer gas in this stellar nursery appear as the wispy structures in an optical image from the Hubble Space Telescope. In between these filaments are giant voids that are filled with hot, X-ray-emitting gas. Astronomers think these bubbles are being blown off the surfaces of the young and massive stars throughout NGC 604. NGC 604 also likely contains an extreme member of the class of colliding-wind binaries, as reported in a recent paper led by Kristen Garofali of the University of Arkansas in Fayetteville, Arkansas. It is the first candidate source in this class to be discovered in M33 and the most distant example known, and shares several properties with the famous, volatile system called Eta Carinae, located in our galaxy. Chandra's X-ray data (blue) are com-bined in this image with optical data from Hubble (purple). G292: Supernova remnants are the debris from exploded stars. G292.0+1.8 is a rare type of supernova remnant observed to contain large amounts of oxygen. Because they are one of the primary sources of the heavy elements (that is, everything other than hydrogen and helium) necessary to form planets and people, these oxygen-rich supernova remnants are important to study. The X-ray image of G292+1.8 from Chandra shows a rapidly expanding, intricately structured field left behind by the shattered star. The image is colored red, green, teal and purple in X-rays ranging from the lowest to highest energy levels. Recently the first detection was made of iron debris from the exploded star, as reported in a paper led by Jayant Bhalerao of the University of Texas at Arlington in Texas. They construct-ed a map of this debris, along with that of silicon and sulphur, to understand more about the explosion. They found that these three elements are mainly located in the upper right of the remnant. This is in the opposite direction from the neutron star that was formed in the explosion, and was then kicked towards the lower left of the remnant. This suggests that the origin of this kick is gravitational and fluid forces from an asymmetric explosion. If more than half of the star's debris is ejected in one direction, then the neutron star is kicked in the other direction so that momen-tum is conserved. This finding argues against the idea that the copious amounts of neutrinos formed in the superno-va explosion were emitted in a lop-sided direction, imparting a kick to the neutron star.
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A lack of mysterious deaths from hypothetical ‘macros’ suggests dark matter is small and light by Lisa Grossman
The fact that no one seems to have been killed by speeding blobs of dark matter puts limits on how large and dead-ly these particles can be, a study suggests. “In the last 30 years, if someone had died of this, we would have heard of it,” says physicist Glenn Starkman of Case Western Reserve University in Cleveland.
Physicists think the invisible dark matter must exist because they can see its gravitational effects on visible matter throughout the cosmos. But no one knows what it’s actually made of. Among the leading candidates are weakly interacting massive particles, or WIMPs, but scientists have hunted for them for decades with no success.
So physicists are turning to other theoretical candidates. Starkman and colleagues focused on macroscopic dark matter, or macros, first proposed by physicist Edward Witten in the 1980s. If they exist, macros would be made up of subatomic particles called quarks, just like ordinary matter, but combined in a way never before observed. Theo-retically, macros could have almost any size and mass. And because dark matter doesn’t interact with regular mat-ter, there would be nothing to stop these particles from zipping around unimpeded. So Starkman — along with Case Western physicist Jagjit Singh Sidhu and physicist Robert Scherrer of Vanderbilt University in Nashville — decided to do a gut check using human flesh as a dark matter detector. If a macro as small as a square micrometer zipped through your body at hypersonic speed, it would deposit about as much energy in your body as a typical metal bul-let, the team calculated. But the damage it caused would be different from that of a bullet: A macro would heat the cylinder of tissue in its wake to about 10,000,000° Celsius — vaporizing the tissue and leaving a path of plasma.
“It’s like if you were in Star Wars, and a Jedi hit you with their lightsaber, or someone shot you with their phaser [gun],” Starkman says. There would be nothing you could do to shield yourself from such a macro strike. Still, there’s no reason to worry, Starkman says. Considering there have been no reports of anyone suddenly suffering a mysterious lightsaber wound, the researchers concluded that if macros exist, they have to be smaller than a mi-crometer and lighter than about 50 kilograms.
“The odds of dying from this are less than 1 in 100 million,” Starkman says. As wacky as this might sound, physicist Katherine Freese thought these calculations were worth doing. “This study is fun,” says Freese of the University of Michigan in Ann Arbor. “Looking for macros in already existing detectors, such as the human body, is a good idea.” Though she wasn’t involved in the macro research, she and colleagues did a similar thought experiment with WIMPs in 2012. “But weak interactions are so weak as to be harmless” to human bodies. Next, Starkman and Sidhu plan to look for macro tracks in slabs of granite, which would appear as cylinders of black obsidian running straight through the rock. They’re starting with a cemetery near the Case Western campus.
Hypothetical dark matter particles called “macros” could stream through space and constantly bombard Earth. Some could seriously injure any unlucky humans they pass through, but a lack of mysterious deaths suggests the biggest potential macros don’t exist. PL-Caltech/NASA
Moon Aug 5
For observers in the middle northern latitudes, this chart is suitable for early August at 11 p.m. or late August near 10 p.m.
The Ecliptic representsthe plane of the solar system. The sun, the moon, and the major planets all lie on or near this imaginary line in the sky. Relative size of the full moon.
The stars plotted represent those which can be seen from areas suffering
from moderate light pollution. In larger cities, less than
100 stars are visible, while from dark,rural areas well
over ten times that amount
are found.
Navigating the mid August night sky: Simply start with what you know or with what you can easily find.
1234
Pointer Stars to the North Star
South
North
West
Arcturus
Spica
Vega
Deneb
Altair
Polaris, the North Star
CygnusPegasus
Androm
eda
Cep
heus
Cassi
opeia
Aquila
1
2
34
B
Astronomical League www.astroleague.org/outreach; duplication is allowed and encouraged for all free distribution.
Relative sizes and distances in the sky can
be deceiving. For instance, 360 "full
moons" can be placed side by side, extending from
horizon to horizon.
Navigating the mid August Night Sky
Binocular HighlightsA: On the western side of the Keystone glows the Great Hercules Cluster.B: Between the bright stars Antares and Altair, hides an area containing many star clusters and nebulae.C: 40% of the way between Altair and Vega, twinkles the "Coathanger," a group of stars outlining a coathanger.D: Sweep along the Milky Way for an astounding number of faint glows and dark bays, including the Great Rift.E: The three westernmost stars of Cassiopeia's "W" point south to M31, the Andromeda Galaxy, a "fuzzy" oval.
Antares
Zubenelgenubi – nice binocular double star
Mizar/Alcor – nice binocular double star
Omega Scorpii – nice binocular double star
+
Jupiter
Milk
y W
ay
The Northern
Crown
The Teapot
Numerous star clusters and nebulae
Extend a line north from the two stars at the tip of the Big Dipper's bowl. It passes by Polaris, the North Star.Follow the arc of the Dipper's handle. It intersects Arcturus, the brightest star in the June evening sky.To the northeast of Arcturus shines another star of the same brightness, Vega. Draw a line from Arcturus to Vega. It first meets "The Northern Crown," then the "Keystone of Hercules." A dark sky is needed to see these two dim stellar configurations.High in the East lies the summer triangle stars of Vega, Altair, and Deneb.
SummerTriangle
The Great Square
ScorpiusSagittarius
CoathangerCluster
Great RiftZ
enit
h
+M31
A
C
D
D
D
E
M13
East
Saturn
The Keystone of Hercules
Radiant of the
Perseid Meteor Shower
Best after 4 a.m. Aug. 13