** What’s Up: October 2022 Skywatching Tips from NASA – NASA JPL
What are some skywatching highlights in October 2022? Enjoy giant planets Jupiter and Saturn all night throughout the month. Then watch as Mars begins its retrograde motion, moving westward each night instead of eastward, for the next few months. Finally, check out the Orionid meteors overnight on Oct. 20.
0:00 Intro 0:11 Evenings with Jupiter & Saturn 0:37 Mars’ retrograde motion 2:07 Orionid meteor shower 3:04 October Moon phases
Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/skywatch…
Crisp, clear October nights are full of celestial showpieces. Find Pegasus, the flying horse of Greek myth, to pinpoint dense globular star clusters and galaxies, and keep watching for space-based views of M15, NGC 7331, and the Andromeda Galaxy.
What’s in the night sky tonight? Get ready for Mars opposition, make the most of Uranus (and prepare for a lunar occultation at the end of the year), observe Neptune following its September opposition, see Jupiter’s Galilean moons, take in the Orionid meteor shower and admire the Summer Triangle asterism.
Our monthly Sky Tour #astronomy #podcast provides an informative and entertaining 10-minute guided tour of the nighttime sky. Listen to the October episode and give #Jupiter a really close look, learn what #Andromeda and #Pegasus have in common, circle around the pole #star #Polaris, and watch for #meteors shed by #Halley’s #Comet
This shows a still image of the supermassive black hole Sagittarius A*, as seen by the Event Horizon Collaboration (EHT), with an artist’s illustration indicating where the modelling of the ALMA data predicts the hot spot to be and its orbit around the black hole. Credits: ESO
Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have spotted signs of a ‘hot spot’ orbiting Sagittarius A*, the black hole at the centre of our galaxy. The finding helps us better understand the enigmatic and dynamic environment of our supermassive black hole.
“We think we’re looking at a hot bubble of gas zipping around Sagittarius A* on an orbit similar in size to that of the planet Mercury, but making a full loop in just around 70 minutes. This requires a mind blowing velocity of about 30% of the speed of light!”
says Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who led the study published today in Astronomy & Astrophysics.
The observations were made with ALMA in the Chilean Andes — a radio telescope co-owned by the European Southern Observatory (ESO) — during a campaign by the Event Horizon Telescope (EHT) Collaboration to image black holes. In April 2017 the EHT linked together eight existing radio telescopes worldwide, including ALMA, resulting in the recently released first ever image of Sagittarius A*. To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used ALMA data recorded simultaneously with the EHT observations of Sagittarius A*. To the team’s surprise, there were more clues to the nature of the black hole hidden in the ALMA-only measurements.
By chance, some of the observations were done shortly after a burst or flare of X-ray energy was emitted from the centre of our galaxy, which was spotted by NASA’s Chandra Space Telescope. These kinds of flares, previously observed with X-ray and infrared telescopes, are thought to be associated with so-called ‘hot spots’, hot gas bubbles that orbit very fast and close to the black hole.
“What is really new and interesting is that such flares were so far only clearly present in X-ray and infrared observations of Sagittarius A*. Here we see for the first time a very strong indication that orbiting hot spots are also present in radio observations,”
says Wielgus, who is also affiliated with the Nicolaus Copernicus Astronomical Centre, Poland and the Black Hole Initiative at Harvard University, USA.
“Perhaps these hot spots detected at infrared wavelengths are a manifestation of the same physical phenomenon: as infrared-emitting hot spots cool down, they become visible at longer wavelengths, like the ones observed by ALMA and the EHT,”
adds Jesse Vos, a PhD student at Radboud University, the Netherlands, who was also involved in this study.
The flares were long thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*, and the new findings support this idea.
“Now we find strong evidence for a magnetic origin of these flares and our observations give us a clue about the geometry of the process. The new data are extremely helpful for building a theoretical interpretation of these events,”
says co-author Monika Mościbrodzka from Radboud University.
This visible light wide-field view shows the rich star clouds in the constellation of Sagittarius (the Archer) in the direction of the centre of our Milky Way galaxy. The entire image is filled with vast numbers of stars — but far more remain hidden behind clouds of dust and are only revealed in infrared images. This view was created from photographs in red and blue light and form part of the Digitized Sky Survey 2. The field of view is approximately 3.5 degrees x 3.6 degrees. Credits: ESO
ALMA allows astronomers to study polarised radio emission from Sagittarius A*, which can be used to unveil the black hole’s magnetic field. The team used these observations together with theoretical models to learn more about the formation of the hot spot and the environment it is embedded in, including the magnetic field around Sagittarius A*. Their research provides stronger constraints on the shape of this magnetic field than previous observations, helping astronomers uncover the nature of our black hole and its surroundings.
The observations confirm some of the previous discoveries made by the GRAVITY instrument at ESO’s Very Large Telescope (VLT), which observes in the infrared. The data from GRAVITY and ALMA both suggest the flare originates in a clump of gas swirling around the black hole at about 30% of the speed of light in a clockwise direction in the sky, with the orbit of the hot spot being nearly face-on.
“In the future we should be able to track hot spots across frequencies using coordinated multiwavelength observations with both GRAVITY and ALMA — the success of such an endeavour would be a true milestone for our understanding of the physics of flares in the Galactic centre,”
says Ivan Marti-Vidal of the University of València in Spain, co-author of the study.
The team is also hoping to be able to directly observe the orbiting gas clumps with the EHT, to probe ever closer to the black hole and learn more about it.
“Hopefully, one day, we will be comfortable saying that we ‘know’ what is going on in Sagittarius A*,”
Wielgus concludes.
This image shows the Atacama Large Millimeter/submillimeter Array (ALMA) looking up at the Milky Way as well as the location of Sagittarius A*, the supermassive black hole at our galactic centre. Highlighted in the box is the image of Sagittarius A* taken by the Event Horizon Telescope (EHT) Collaboration. Located in the Atacama Desert in Chile, ALMA is the most sensitive of all the observatories in the EHT array, and ESO is a co-owner of ALMA on behalf of its European Member States. Credits: ESO
** What’s Up: September 2022 Skywatching Tips from NASA – NASA JPL
What are some skywatching highlights in September 2022? Mars is on the move this month, forming a “red triangle” with bright red stars Aldebaran and Betelgeuse. Saturn and Jupiter fly with the Moon on the 9th, and then the Moon slides over closer Jupiter in the morning sky on the 11th. At the end of the month, September 23rd brings the equinox, meaning day and night are of nearly equal length, and a change of seasons is afoot.
0:00 Intro 0:12 Mars on the move in September 0:43 Jupiter at opposition 1:39 Evening planets: Jupiter and Saturn 2:07 September equinox 2:55 September Moon phases
Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/skywatch….
In September, Pegasus becomes increasingly prominent in the southeastern sky, allowing stargazers to locate globular star clusters and a nearby double star, Alpha Capricorni. Keep watching for space-based views of densely packed, spherical collections of ancient stars in visible and X-ray light.
What can you see in the sky tonight? Astronomers Pete Lawrence and Paul Abel reveal the planets, stars and deep-sky objects visible in the night sky over the coming weeks.
Our monthly Sky Tour #astronomy #podcast provides an informative and entertaining 10-minute guided tour of the nighttime sky. Listen to the September episode to learn about the upcoming #equinox, the harvest #Moon, and the #stars of the #summertriangle.
Listen and subscribe to this podcast at https://skyandtelescope.org/observing/ and don’t forget to subscribe to S&T’s YouTube channel to get alerts about new videos, including this monthly podcast.
** What’s Up: August 2022 Skywatching Tips from NASA – NASA JPL
What are some skywatching highlights in August 2022? The daily parade of four naked-eye planets in the mornings comes to an end this month. But there are still lots of great highlights, especially if you have access to binoculars. Plus, Saturn and Jupiter are returning to nighttime skies! The outlook for the Perseid meteors isn’t great due to a full moon on the peak night of August 12, but still it’s worth keeping an eye out for early Perseids after midnight the week before. And August is a great month to learn an easy-to-spot constellation – Cygnus the swan.
0:00 Intro 0:11 Planet-watching highlights 1:56 Perseid meteors outlook 2:34 The constellation Cygnus 3:45 August Moon phases
Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/skywatch….
In August, a flock of star-studded figures soars overhead. Look for the Vega and Lyra constellations, which point to Epsilon Lyrae and the Ring Nebula. You can also spot three bright summer stars: Vega, Deneb, and Altair, which form the Summer Triangle. Keep watching for space-based views of these and other stars and nebulas.
About this Series “Tonight’s Sky” is a monthly video of constellations you can observe in the night sky. The series is produced by the Space Telescope Science Institute, home of science operations for the Hubble Space Telescope, in partnership with NASA’s Universe of Learning. This is a recurring show, and you can find more episodes—and other astronomy videos—at https://hubblesite.org/resource-galle….
What’s in the night sky tonight? Pete Lawrence and Paul Abel reveal the stars, constellations, planets, conjunctions and deep-sky objects worth keeping an eye on in August.
Our monthly Sky Tour #astronomy #podcast provides an informative and entertaining 10-minute guided tour of the nighttime sky. Listen to the August episode to learn about the #shootingstars of the #Perseids, how to spot #Saturn, and tour the #stars of #summer.
This artist’s impression shows what the binary system VFTS 243 might look like if we were observing it up close. The system, which is located in the Tarantula Nebula in the Large Magellanic Cloud, is composed of a hot, blue star with 25 times the Sun’s mass and a black hole, which is at least nine times the mass of the Sun. The sizes of the two binary components are not to scale: in reality, the blue star is about 200 000 times larger than the black hole. Note that the ‘lensing’ effect around the black hole is shown for illustration purposes only, to make this dark object more noticeable in the image. The inclination of the system means that, when looking at it from Earth, we cannot observe the black hole eclipsing the star.
A team of international experts, renowned for debunking several black hole discoveries, have found a stellar-mass black hole in the Large Magellanic Cloud, a neighbour galaxy to our own.
“For the first time, our team got together to report on a black hole discovery, instead of rejecting one,”
says study leader Tomer Shenar. Moreover, they found that the star that gave rise to the black hole vanished without any sign of a powerful explosion. The discovery was made thanks to six years of observations obtained with the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT).
“We identified a ‘needle in a haystack’,”
says Shenar who started the study at KU Leuven in Belgium [1] and is now a Marie-Curie Fellow at Amsterdam University, the Netherlands. Though other similar black hole candidates have been proposed, the team claims this is the first ‘dormant’ stellar-mass black hole to be unambiguously detected outside our galaxy.
Stellar-mass black holes are formed when massive stars reach the end of their lives and collapse under their own gravity. In a binary, a system of two stars revolving around each other, this process leaves behind a black hole in orbit with a luminous companion star. The black hole is ‘dormant’ if it does not emit high levels of X-ray radiation, which is how such black holes are typically detected.
“It is incredible that we hardly know of any dormant black holes, given how common astronomers believe them to be”,
explains co-author Pablo Marchant of KU Leuven. The newly found black hole is at least nine times the mass of our Sun, and orbits a hot, blue star weighing 25 times the Sun’s mass.
Glowing brightly about 160 000 light-years away, the Tarantula Nebula is the most spectacular feature of the Large Magellanic Cloud, a satellite galaxy to our Milky Way. This image from VLT Survey Telescope at ESO’s Paranal Observatory in Chile shows the region and its rich surroundings in great detail. It reveals a cosmic landscape of star clusters, glowing gas clouds and the scattered remains of supernova explosions.
Dormant black holes are particularly hard to spot since they do not interact much with their surroundings.
“For more than two years now, we have been looking for such black-hole-binary systems,”
says co-author Julia Bodensteiner, a research fellow at ESO in Germany.
“I was very excited when I heard about VFTS 243, which in my opinion is the most convincing candidate reported to date.” [2]
To find VFTS 243, the collaboration searched nearly 1000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud, looking for the ones that could have black holes as companions. Identifying these companions as black holes is extremely difficult, as so many alternative possibilities exist.
“As a researcher who has debunked potential black holes in recent years, I was extremely skeptical regarding this discovery,”
says Shenar. The skepticism was shared by co-author Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian in the USA, whom Shenar calls the “black hole destroyer”.
“When Tomer asked me to double check his findings, I had my doubts. But I could not find a plausible explanation for the data that did not involve a black hole,”
explains El-Badry.
This composite image shows the star-forming region 30 Doradus, also known as the Tarantula Nebula. The background image, taken in the infrared, is itself a composite: it was captured by the HAWK-I instrument on ESO’s Very Large Telescope (VLT) and the Visible and Infrared Survey Telescope for Astronomy (VISTA), shows bright stars and light, pinkish clouds of hot gas. The bright red-yellow streaks that have been superimposed on the image come from radio observations taken by the Atacama Large Millimeter/submillimeter Array (ALMA), revealing regions of cold, dense gas which have the potential to collapse and form stars. The unique web-like structure of the gas clouds led astronomers to the nebula’s spidery nickname.
The discovery also allows the team a unique view into the processes that accompany the formation of black holes. Astronomers believe that a stellar-mass black hole forms as the core of a dying massive star collapses, but it remains uncertain whether or not this is accompanied by a powerful supernova explosion.
“The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion,” explains Shenar. “Evidence for this ‘direct-collapse’ scenario has been emerging recently, but our study arguably provides one of the most direct indications. This has enormous implications for the origin of black-hole mergers in the cosmos.“
The black hole in VFTS 243 was found using six years of observations of the Tarantula Nebula by the Fibre Large Array Multi Element Spectrograph (FLAMES) instrument on ESO’s VLT[3].
Despite the nickname ‘black hole police’, the team actively encourages scrutiny, and hopes that their work, published today in Nature Astronomy, will enable the discovery of other stellar-mass black holes orbiting massive stars, thousands of which are predicted to exist in Milky Way and in the Magellanic Clouds.
“Of course I expect others in the field to pore over our analysis carefully, and to try to cook up alternative models,” concludes El-Badry. “It’s a very exciting project to be involved in.”
Notes
[1] The work was conducted in the team lead by Hugues Sana at KU Leuven’s Institute of Astronomy.
[2] A separate study led by Laurent Mahy, involving many of the same team members and accepted for publication in Astronomy & Astrophysics, reports on another promising stellar-mass black hole candidate, in the HD 130298 system in our own Milky Way galaxy.
[3] The observations used in the study cover about six years: they consist of data from the VLT FLAMES Tarantula Survey (led by Chris Evans, United Kingdom Astronomy Technology Centre, STFC, Royal Observatory, Edinburgh; now at the European Space Agency) obtained from 2008 and 2009, and additional data from the Tarantula Massive Binary Monitoring programme (led by Hugues Sana, KU Leuven), obtained between 2012 and 2014.
