Astronomy Now is the UK’s biggest astronomy magazine, with 132 feature-packed pages. Since 1987 it has been essential reading for astronomers in the UK and around the world. Each month, the magazine contains features, reviews, news and practical guides on all aspects of astronomy.
The starburst galaxy M94, also known as NGC 4736, resides in the northern constellation Canes Venatici at a distance of about 16 million light years. The galaxy has a diameter of about 33,000 light years and is a member of the Virgo cluster, receding from the Milky way at about 337 kilometres (220 miles) per second.
M94 has two distinct ring structures: an inner “starburst” ring, seen here in a closeup by the Hubble Space Telescope in 2015, and a fainter outer ring with regions of moderate star formation. The bluish inner ring features countless hot, young stars forming in the wake of a pressure wave seeping outward from the core. The pressure wave compresses gas and dust as it passes, causing the material to collapse into denser clouds that eventually reach temperatures triggering nuclear fusion and star birth. M94’s ring structure could be the result of a merger with another galaxy or gravitational interactions with other members of the Virgo cluster.
Messier 94, a starburst galaxy, features two distinct rings where pressure waves sweeping outward from the core have triggered rapid star formation. This view from the Hubble Space Telescope shows the core and the inner starburst ring. Image: ESA/Hubble & NASA
Astronomers have discovered a dozen new moons orbiting Jupiter, including one “oddball” in an orbit that eventually could lead to a head-on collision. Image: Carnegie Institution for Science
Astronomers peering into the depths of the solar system in search of a presumed ninth planet far beyond Pluto happened to be looking past Jupiter during their observations and happened to discovery 12 new moons orbiting the giant planet.
“Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant solar system objects, so we were serendipitously able to look for new moons around Jupiter while at the same time looking for planets at the fringes of our solar system,” said the Carnegie Institution’s Scott Sheppard.
A team led by Sheppard initially spotted the moons in 2017 while scanning the outer solar system in search of “Planet X,” a hypothesised world thought to be responsible for the observed orbits of several bodies in the remote Kuiper Belt. In 2014,
Sheppard, Dave Tholen of the University of Hawaii and Chad Trujillo of Northern Arizona University discovered the most distant known solar system body and were among the first to consider the possibility of a massive, undetected planet beyond Pluto, a claim shared by veteran planet hunder Mike Brown and his colleagues at the California Institute of Technology.
The newly discovered Jupiter moons, with diameters of one to three kilometres (0.62 to 1.9 miles), required multiple observations to verify.
Nine of the moons are part of an outer “swarm” that orbit in the opposite, or retrograde, direction of Jupiter’s spin, taking about two years to complete one trip around the planet. The moons orbit in three different groupings and are thought to be the remnants of three bodies that were broken apart in earlier collisions.
Two other new moons were found to be part of a closer group that orbits in the prograde, or same direction as Jupiter’s rotation. They also are thought to be the result of an earlier collision and take about a year to complete one orbit.
The 12th new moon is a bit of an oddball, Sheppard said, with “an orbit like no other known Jovian moon. It’s also likely Jupiter’s smallest known moon, being less than one kilometre in diameter.”
The moon orbits in the prograde direction, but at a greater distance from Jupiter with an orbital period of about a year and a half. As such, the orbit crosses those of the more distant retrograde moons, raising the possibility of a possible head-on collision at some point in the future.
“This is an unstable situation,” said Sheppard. “Head-on collisions would quickly break apart and grind the objects down to dust.”
Most of the discoveries were made with the Dark Energy Camera on the Blanco 4-metre telescope at Cerro Tololo Inter-American in Chile, operated by the National Optical Astronomical Observatory of the United States. Confirmation came with help from a variety of observatories, including the 6.5-metre Magellan telescope at Carnegie’s Las Campanas Observatory in Chile, the 4-metre Discovery Channel Telescope at Lowell Observatory in Arizona, the 2.2-metre University of Hawaii telescope and the 8-metre Subaru and Gemini Telescopes, also in Hawaii.
An artist’s impression of a neutron star being torn apart as it merges with a black hole, producing gravitational waves that could help astronomers come up with a more accurate value for the Hubble constant, a measure of how fast the Universe is expanding. Image: A. Tonita, L. Rezzolla, F. Pannarale
Researchers using different techniques to measure how fast the universe is expanding have come up with two different answers, a conflict that so far has resisted explanation. Researchers at the Massachusetts Institute of Technology say the conflict may be resolved by analysis of gravitational waves from neutron star-black hole mergers, resulting in a value for the Hubble constant, a measure of the Universe’s expansion, that is more precise than earlier results.
The only problem? No such mergers have yet been detected. But astronomers are hopeful the Laser Interferometry Gravitational Wave Observatory, or LIGO, will detect such mergers when it resumes operations early next year with upgraded, more sensitive components.
“So far, people have focused on binary neutron stars as a way of measuring the Hubble constant with gravitational waves,” said Salvatore Vitale, assistant professor of physics at MIT and lead author of the paper in Physical Review Letters. “We’ve shown there is another type of gravitational wave source which so far has not been exploited as much: black holes and neutron stars spiralling together.”
The Hubble constant is an indicator of how fast the universe is expanding. Researchers using the Hubble Space Telescope and the European Space Agency’s Gaia spacecraft to precisely measure the distances to Cepheid variable stars in the Milky Way and nearby galaxies have come up with a value of 73.5 kilometres (45.6 miles) per second per million parses.
Put another way, for every 3.3 million light years – 1 megaparsec – objects are moving away an additional 73.5 kilometres per second faster. The uncertainty in the measurement is just 2.2 percent.
But astronomers using ESA’s Planck spacecraft to study conditions in the extremely early universe came up with a value of 67 kilometres per second per megaparsec. The cause of the discrepancy is not yet known.
“That’s where LIGO comes into the game,” Vitale says. “Gravitational waves provide a very direct and easy way of measuring the distances of their sources. What we detect with LIGO is a direct imprint of the distance to the source, without any extra analysis.”
The bulk of the gravitational waves emitted in neutron star mergers originate at the center of the coalescing disk with smaller amounts originating from the edges, MIT said in a release describing the study. A strong, or “loud,” gravitational wave signal from the merger of two neutron stars could indicate waves from the edges of a nearby system or from the center of a much more distant source.
“With neutron star binaries, it’s very hard to distinguish between these two situations,” Vitale says.
But a neutron star-black hole merger is another matter. Computer analysis indicates that even if rare, they have the potential to produce signals that could result in extremely precise distance measurements based on the spin of the black hole around the captive neutron star.
“LIGO will start taking data again in January 2019, and it will be much more sensitive, meaning we’ll be able to see objects farther away,” Vitale said. “So LIGO should see at least one black hole-neutron star binary, and as many as 25, which will help resolve the existing tension in the measurement of the Hubble constant, hopefully in the next few years.”
The Virgo galaxy cluster if familiar to amateur and professional astronomers alike, a rich collection of more than 1,300 galaxies, including dozens within the reach of relatively small telescopes. NGC 4388, captured here by the Hubble Space Telescope in 2016, is an intriguing member of the cluster, undergoing a transformation of sorts due to gravitational interactions with other members of the group. The outskirts of NGC 4388 appear relatively smooth and featureless, familiar aspects of elliptical galaxies, but symmetric spiral arms extend from the galaxy’s core, with bright blue concentrations indicating areas of recent star formation.
“Despite the mixed messages, NGC 4388 is classified as a spiral galaxy,” according to the European Space Agency’s Hubble web page. “Its unusual combination of features are thought to have been caused by interactions between NGC 4388 and the Virgo Cluster. Gravitational interactions — from glancing blows to head-on collisions, tidal influencing, mergers and galactic cannibalism — can be devastating to galaxies. While some may be lucky enough to simply suffer a distorted spiral arm or newly-triggered wave of star formation, others see their structure and contents completely and irrevocably altered.
A galaxy in the Virgo cluster that is being transformed by gravitational interactions with others in the rich collection. Image: ESA/Hubble & NASA
A stunning view of the Milky Way’s fiery heart where a super-massive black hole lurks amid strange filamentary structures. Image: South African Radio Astronomy Observatory.
South Africa’s newly inaugurated 64-dish MeerKAT radio telescope, a precursor to the Square Kilometre Array, has imaged the heart of the Milky Way in unprecedented detail, revealing long, magnetised filaments and the blazing core where a supermassive black hole lurks unseen at optical wavelengths.
“We wanted to show the science capabilities of this new instrument,” said Fernando Camilo, chief scientist at the South African Radio Astronomy Observatory. “The centre of the galaxy was an obvious target: unique, visually striking and full of unexplained phenomena, but also notoriously hard to image using radio telescopes. Although it’s early days with MeerKAT, and a lot remains to be optimised, we decided to go for it – and were stunned by the results.”
Built by the SARAO and inaugurated 13 July by Deputy President David Mabuza, MeerKAT’s 64 dishes eventually will be part of the Square Kilometre Array, the world’s largest radio telescope with hundreds of distributed dishes in Australia and South Africa. As it stands, MeerKAT’s dishes provide 2,000 unique antenna pairs, “resulting in high-fidelity images of the radio sky,” the SARAO said in a news release.
Earth’s Sun orbits the galaxy’s core at a distance of some 25,000 light years. While intervening gas and dust shroud the hidden heart of the galaxy where a super-massive black hole is known to reside, radio waves pass through to provide a glimpse of its hidden features. MeerKAT’s initial observations provide a tantalising hint of things to come.
Of special interest are long magnetised filaments discovered in the 1980s that are seen near the central black hole and nowhere else. Their origin is a mystery.
“The MeerKAT image has such clarity,” marvelled Farhad Yusef-Zadeh of Northwestern University in the United States, an expert on the filamentary structures seen near the central black hole. “The image shows so many features never before seen, including compact sources associated with some of the filaments, that it could provide the key to cracking the code and solve this three-decade riddle.”
The circle indicates a previously unseen hot spot on Jupiter’s moon Io that may indicate a newly formed volcano. Image: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
NASA”s Juno spacecraft now orbiting Jupiter has spotted what may be a previously undiscovered volcano on the small moon Io, the most geologically active body in the solar system. The data were collected by Juno’s Jovian InfraRed Auroral Mapper, or JIRAM, instrument on 16 December 2017 when the spacecraft was at a distance of 470,000 kilometres (290,000 miles).
“The new Io hotspot JIRAM picked up is about 200 miles (300 kilometres) from the nearest previously mapped hotspot,” said Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics in Rome. “We are not ruling out movement or modification of a previously discovered hot spot, but it is difficult to imagine one could travel such a distance and still be considered the same feature.”
According to NASA, Io’s surface “is covered by sulphur in different colourful forms. As Io travels in its slightly elliptical orbit, Jupiter’s immense gravity causes ‘tides’ in the solid surface that rise 300 feet (100 meters) high on Io, generating enough heat for volcanic activity and to drive off any water. Io’s volcanoes are driven by hot silicate magma.”
Juno’s instruments will continue to monitor the moon during even closer flybys planned later in its mission. During previous missions by NASA’s Voyager probes, the Galileo orbiter, the Saturn-bound Cassini and and the New Horizons probe that flew past Pluto, some 150 active volcanoes were discovered with another 250 hot spots representing apparent volcanism.
Using precise distance measurements to nearby Cepheid variable stars collected by ESA’s Gaia spacecraft, astronomers using the Hubble Space Telescope were able to calibrate the brightness of Cepheids in remote galaxies to help determine the most accurate value yet for the Hubble constant, a measure of how fast the universe is expanding. But the data do not agree with the value derived from studies of the extremely early Universe. Image: NASA, ESA, and A. Feild (STScI)
Astronomers measuring how fast the cosmos is expanding in the wake of the Big Bang are struggling to explain a baffling conflict between the value observed today and the value derived from observations of the extremely early Universe.
Using the Hubble Space Telescope and the European Space Agency’s Gaia observatory, researchers calculated a value for the Hubble constant, a measure of the expansion rate of the Universe, of 73.5 kilometres (45.6 miles) per second per million parses. That means that for every 3.3 million light years – 1 million parsecs – farther away a galaxy might be, it is moving away from us 73.5 kilometres per second faster.
The measurement is remarkably precise, with an uncertainty of just 2.2 percent.
But results from ESA’s Planck spacecraft, based on observations of the microwave background radiation, the residual heat left over after the Big Bang, place the value of the Hubble constant at 67 kilometres per second per megaparsec.
While that might seem like generally good agreement for such esoteric measurements, the gap between the Hubble-Gaia data and the Planck measurement is about four times the size of their combined uncertainty. That indicates “a full-blown incompatibility between our views of the early and late time universe,” said Adam Riess, a Nobel Laureate at the Space Telescope Science Institute who helped discover dark energy.
“At this point, clearly it’s not simply some gross error in any one measurement,” he added. “It’s as though you predicted how tall a child would become from a growth chart and then found the adult he or she became greatly exceeded the prediction. We are perplexed.”
George Efstathiou of the Kavli Institute for Cosmology in Cambridge, England, and a Planck team member who was not involved in the research agreed, saying “we now have a serious tension with the cosmic microwave background data.”
The Planck-derived value of the Hubble constant is based on the spacecraft’s precise observations of the cosmic background radiation dating back to within a few hundred thousand years of the Big Bang. Those observations, plugged into the “standard model” of physics, allowed researchers to extrapolate the present expansion rate.
The Hubble-Gaia conclusions were based on a different technique, the direct observation of Cepheid variable stars close to home and in remote galaxies. Cepheids pulsate in a predictable manner that indicates their true brightness. By observing the apparent brightness of a Cepheid in a distant galaxy, astronomers can compute how far away the star must be.
Gaia provided the most accurate data yet on 50 Cepheids in the Milky Way. That allowed the Hubble astronomers to carefully calibrate their observations of extra-galactic Cepheids.
Comparing the positions of those stars and galaxies with the expansion of space as indicated by the red shifting of light from nearby galaxies, Riess’ team was able to derive an outward velocity at different points and from that, the Hubble constant.
“Gaia is the new gold standard for calibrating distance,” said Stefano Casertano of Space Telescope Science Institute. “Gaia brings a new ability to recalibrate all past distance measures, and it seems to confirm our previous work. We get the same answer for the Hubble constant if we replace all previous calibrations of the distance ladder with just the Gaia parallaxes. It’s a crosscheck between two very powerful and precise observatories.”
Riess’ team hopes to reduce the uncertainty in its value for the Hubble constant to less than 1 percent by the early 2020s. Explaining the discrepancy with the Planck data is another matter.
An artist’s impression of a super-massive black hole at the heart of a blazar galaxy shooting a high-energy beam of radiation into space. A neutrino detected in Antarctica has been traced back to a blazar in the constellation Orion, providing an explanation high-energy cosmic rays that have baffled astronomers for decades. Image: DESY, Science Communication Lab
An international team of astronomers has traced a ghostly neutrino back to its source, a spinning super-massive black hole at the heart of a “blazar” galaxy some four billion light years away. The detection and follow-up observations provide a convincing explanation for a mystery that has endured for more than a century: what is the source of the high-energy cosmic rays constantly raining down on Earth from deep space?
The initial detection by the IceCube Neutrino Observatory in Antarctica, and subsequent observations of high energy radiation from the same source by space telescopes and ground-based observatories, indicate such black holes act as the particle accelerators responsible for at least some of those cosmic rays.
“The evidence for the observation of the first known source of high-energy neutrinos and cosmic rays is compelling,” said Francis Halzen, a University of Wisconsin–Madison professor of physics and the lead scientist for the IceCube Neutrino Observatory.
Two papers published this week in the journal Science discuss the neutrino detection, follow-up observations and interpretation of the data.
Tracing the path of an electrically charged cosmic ray particles is not possible because the trajectory is affected by magnetic fields. But neutrinos have little or no mass, travel at nearly the speed of light, are not electrically charged and rarely interact with normal matter. As a result, their trajectories through space are not affected by magnetic fields or passage through gas, dust or even planets.
As a result, the neutrino detected by the IceCube observatory at the Amundsan-Scott South Pole Station on 22 September, 2017, could be traced back to a specific point in the sky, a galaxy in the constellation Orion known as TXS-0506+056 that is some four billion light years from Earth. The galaxy is a known blazar, that is, one harbouring a super-massive black hole that sends out twin jets of high-energy radiation, one of which happens to be aimed at Earth.
Blazars are thought to generate neutrinos and gamma rays, possibly explaining at least one source of cosmic rays. Image: IceCube/NASA
When the neutrino collided with an atomic nucleus at or near the IceCube detector, an automatic alert went out to the astronomical community, triggering multiple searches across the electromagnetic spectrum. NASA’s Fermi gamma ray telescope was the first to detect higher activity from the blazar within 0.06 degrees of the IceCube source. Other instruments operating at optical, radio and X-ray wavelengths also made detections.
“Fermi has been monitoring some 2,000 blazars for a decade, which is how we were able to identify this blazar as the neutrino source,” said Regina Caputo, a coordinator for the Fermi Large Area Telescope collaboration. “High-energy gamma rays can be produced either by accelerated electrons or protons. The observation of a neutrino, which is a hallmark of proton interactions, is the first definitive evidence of proton acceleration by black holes.”
Said Halzen: “Now, we have identified at least one source of cosmic rays because it produces cosmic neutrinos. Neutrinos are the decay products of pions. In order to produce them, you need a proton accelerator.”
Cosmic rays are made up mostly of fast-moving protons accelerated to enormous energies, packing up to 100 times the punch of particles studied in the Large Hadron Collider, the world’s most powerful atom smasher. Theory predicts neutrino emission will be accompanied by gamma radiation, but many questions remain about how blazars are able to boost such particles to such extreme energies.
But the IceCube detection promises to open up a new window on the Universe.
“The ability to globally marshal telescopes to make a discovery using a variety of wavelengths in cooperation with a neutrino detector like IceCube marks a milestone in what scientists call multimessenger astronomy,” Halzen said.
The total lunar eclipse of 27 July 2018 — the longest of the 21st century — is visible from Antarctica, Australasia, Russia (except northernmost parts), Asia, Africa, Scandanavia, Europe (though the Moon rises at mid-eclipse as seen from the centre of the UK) and Central/Eastern South America. This looping animation shows the eclipse’s progress from 1820—2220 UT at ten minute intervals. Astronomical North is up and East is left. AN animation by Ade Ashford.The total lunar eclipse of Friday, 27 July 2018 is the second and last to occur this year (the total lunar eclipse of 31 January was described here). A lunar eclipse occurs when the full Moon passes through the shadow of the Earth and a maximum of five such events can occur in a single year. The eclipse is deemed total if the Moon is fully immersed in the Earth’s central (or umbral) shadow and at such times we can say that we’re experiencing totality.
Schematic diagram of the shadow cast by the Earth. During a total lunar eclipse, the full Moon is shielded from direct illumination by the Sun within the Earth’s central umbral shadow. In contrast, within the penumbral shadow, only a portion of sunlight is blocked. The Moon remains visible within the umbral shadow due to reddened sunlight refracted by the Earth’s atmosphere. Click the graphic for a full-size view. Illustration credit: Sagredo/Public Domain.What’s unusual about the 27 July eclipse is that occurs on the same day that the Moon is farthest from Earth in its orbit, known as apogee. At such times the Moon appears smaller than average and its orbital motion with respect to the stars is slower. These two factors, combined with the fact that the full Moon almost passes through the centre of the Earth’s shadow, means that the duration of totality on 27 July is longer than usual – so great, in fact, that at 104 minutes it’s the longest total lunar eclipse of the entire 21st century*.
Can I see the eclipse from where I live?
Unlike a total solar eclipse that is only visible from a narrow swathe of land or sea where the tip of the Moon’s shadow brushes the surface of the Earth, a total lunar eclipse is visible from an entire hemisphere of our planet where the full Moon happens to be above the horizon. However, not all locations within the Moon-facing hemisphere of Earth will see the entire event as the Moon may rise or set while it is in progress.
Weather permitting, this eclipse can be seen from Antarctica, Australasia, Russia (except northernmost parts), Asia, Africa, Scandanavia, Europe (though the Moon rises at mid-eclipse seen from the centre of the UK) and Central/Eastern South America.Noting the times of the various eclipse stages outlined in the table above, you can consult our interactive online Almanac where you can select your nearest city, type in the Universal Time (UTC) of the appropriate stage and see if the Moon is visible or not. (Almanac tip: ensure that daylight savings time is selected/deselected, as appropriate for your location.)
Viewing prospects from the British Isles
Observers in the UK will miss the first half of the eclipse since the Moon doesn’t rise in the southeast until shortly after 9pm as seen from the heart of the British Isles. (Note from the table above that greatest eclipse occurs at 9:22pm BST.) Furthermore, an observer in the centre of the UK has to wait until just after 9:15pm for sunset, so the sky will be in bright twilight for at least a further 45 minutes. By 10:30pm BST, the Moon will be emerging from the Earth’s umbral shadow, but this is the time to start looking about 6 degrees – roughly half the span of a fist held at arm’s length – below the lunar orb to find magnitude -2.7 Mars, the Red Planet also reaching opposition on this day.
* Note that totality lasted 108 minutes for the lunar eclipse of 16 July 2000, but recall that the 21st century began on 1 January 2001.
The star cluster RCW 38, some 5,500 light years away in the constellation of Vela, features hundreds of massive, hot, young stars embedded in clouds of gas and dust. The stars are generally unseen in optical images but this stunning infrared view, taken with the HAWK instrument attached to the European Southern Observatory’s Very Large Telescope (Unit 4), shows the cluster’s central regions with a bluish tint where young stars and protostars are still in the process of lighting up. Radiation streaming away from these young stars causes surrounding material to glow brightly in contrast to darker, cooler clouds that glow in shades of red and brown. The result, ESO rightly says, is a “spectacular scene – a piece of celestial artwork.”
The star cluster RCW 38, as seen in the infrared by the European Southern Observatory’s Very Large Telescope and HAWK instrument. Credit: ESO/K. Muzic