25 Mar 2017

Astronomers find unexpected, dust-obscured star formation in distant galaxy

Pushing the limits of the largest single-aperture millimetre telescope in the world, and coupling it with gravitational lensing, University of Massachusetts Amherst astronomer Alexandra Pope and colleagues report that they have detected a surprising rate of star formation, four times higher than previously detected, in a dust-obscured galaxy behind a Frontier Fields cluster.

170323125453_1_900x600As Pope explains, "This very distant, relatively typical galaxy is known to us, and we knew it was forming stars, but we had no idea what its real star-formation rate was because there is so much dust surrounding it. Previous observations couldn't reach past that. Finding out that 75 percent of its star formation was obscured by dust is remarkable and intriguing. These observations clearly show that we have more to learn."

She adds, "Historians want to know how civilizations were built up, and we astronomers want to know where and how the elements in the universe were formed and where everything is made of, came from." The study is accepted for publication in The Astrophysical Journal.

The new tool that has made such revelations possible is the 50-meter Large Millimeter Telescope (LMT) which has been observing as a 32-meter telescope located on an extinct volcano in central Mexico in "early science mode" since 2013. Operated jointly by UMass Amherst and Mexico's Instituto Nacional de Astrofísica, Optical y Electronica (INAOE), it offers astonishing new power to peer into dusty galaxies, the astrophysicist says.

Pope, an expert at analysing how dust masks star formation, says tracing dust-obscured galaxies at early epochs offers good signposts for understanding how the universe became enriched with metals over time. "We know at the basic level that metals are formed in stars, but the rate of build-up over cosmic time we don't know," she points out. "We know what we see today but we don't know how it came about, and we want to fill in that picture."

Overall, she and colleagues write, "This remarkable lower-mass galaxy showing signs of both low metallicity and high dust content may challenge our picture of dust production in the early universe."

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Before the AzTEC camera on the LMT took observations of this galaxy, astronomers relied on Hubble Space Telescope images to study star formation, Pope says. But most star formation is obscured by dust, so the Hubble images could not make a complete census of the build-up of stars in this galaxy. "Previous millimetre observations have been limited to the most extreme dusty galaxies. With this study, we have detected a surprisingly high rate of dust-obscured star formation in a typical galaxy in the early universe."

With gravitational lensing, researchers use a foreground mass -- another galaxy or a galaxy cluster -- as a lens. As light from very distant, background galaxies passes through, it is magnified. "This technique offers a way to see things that are much fainter than your telescope can see," she notes. As traced in Hubble images, the lensed galaxy they studied in the Frontier Fields cluster showed it forming only about four solar masses of new stars per year, which is a "fairly typical" observation and unsurprising to astronomers today, Pope says. "But then the LMT observations revealed another 15 solar masses per year, which means we had been missing about three-quarters of the star formation going on."

She adds, "We are not yet at the level of detecting all of the star formation going on, but we are getting better. One of the big goals for us is to push observations at longer wavelengths and to trace these very dusty galaxies at early epochs. We are pushing observations in this direction and the fact that Hubble found only one quarter of the star formation in this distant normal galaxy is a huge motivation for doing a lot more studies like this."

As early as next year, Pope and her colleague Grant Wilson will install on the LMT a new state-of-the-art imaging system he is building, dubbed TolTEC. It will offer mapping speed 100 times faster than the LMT's current capability making it the fastest millimetre-wavelength polarimetric camera on Earth for conducting deep surveys of the universe, Wilson says. It should allow astronomers to create a census of star-forming galaxies, and observations that require five years to complete today will be done in a little over one week.

Pope says, "Currently, our census of dust-obscured star formation activity in galaxies is severely incomplete, especially in the distant universe. With TolTEC on the LMT, we will be able to make a complete census of dust-obscured star formation activity in galaxies over 13 billion years of cosmic time.

24 Mar 2017

NASA to slam a spaceship into an asteroid for practice

2-aidadoublemiNASA and the European Space Agency want to ram into an asteroid in a bid to save humanity from a “Deep Impact”-style catastrophe.

They want to see whether it’s possible to deflect a space rock from its course as part of a planetary defence mission.

Fears over potentially deadly asteroids are at an all time high after the White House issued an “emergency defence plan” in the event of a collision late last year.

Esteemed British astrophysicist and cosmologist Lord Martin Rees recently warned that the government should be spending “millions” on planetary defence.

The proposed mission will use two spacecraft, one to be launched by the ESA in 2020 and the other by NASA in 2021.

The first spaceship, dubbed AIM (for Asteroid Impact Mission) will orbit around 65803 Didymos, which was discovered in 1996.

The NASA spacecraft, called DART (Double Asteroid Redirection Test) will be timed to hit the rock a few months later, at a speed of nearly four miles per second.

AIM’s telescopes will monitor where stray pieces of rock end up.

The mission is to figure out whether deflection is the best defence from a stray space rock.

There’s a danger that crashing into the asteroid could cause fragments to break off and potentially speed up its trajectory.

untitledThe shrapnel could pose a risk to Earth, too.

“When we have a high-speed impact on an asteroid, you create a crater,” explained Andrew Cheng, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland said.

Cheng, who is lead investigator for the NASA side of the project, told Cosmos: “You blow pieces back in the direction you came from.”

The mission is yet to get the green light as it waits to confirm funding.

But planetary defence is a hot topic among scientists.

NASA have previously warned that Earth is “due an extinction level attack”.

But there’s little in place to stop one from causing absolute mayhem.

On the bright side, asteroids fly by Earth regularly and most are small enough to burn up in the atmosphere, completely unnoticed.

2 Mar 2017

There's a Massive, Glowing Blob in the Universe, and a Mystery Source Is Lighting It Up

lya-nebula_1024Astronomers have discovered a vast, glowing blob of gas in the distant Universe, and they can't figure out what's actually lighting it up.

This glowing nebula is located at the centre of an enormous 'protocluster' of early galaxies some 10 billion light-years from Earth, and is the brightest cosmic object of its kind ever found. And yet, there's no obvious source of its power.

The object, called an 'enormous Lyman-alpha nebula' (ELAN), is not only the brightest object of its kind found in the Universe - it's also one of the biggest, rivalling even the 'Slug Nebula', which stretches 2 million light-years through intergalactic space.

"It's extremely bright, and it's probably larger than the Slug Nebula, but there's nothing else visible except the faint smudge of a galaxy," says one of team, J. Xavier Prochaska, from the University of California, Santa Cruz.

"So it's a terrifically energetic phenomenon without an obvious power source."

Only a handful of ELANs have been discovered so far, and these accumulations of gas are thought to be part of a network of filaments that connect neighbouring galaxies to each other in the vast cosmic web of the Universe.

While other ELANs appear to be powered by the intense radiation given off by quasars, star formation, or supernovae, no such events could be found near this latest example, dubbed the MAMMOTH-1 nebula.

What we do know is the light has the same wavelength that's absorbed and emitted by hydrogen atoms as they cool down - a discharge known as Lyman-alpha radiation - but it's not clear what's been heating them up.

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The find recalls a discovery in 2000 of another ELAN, known as the Lyman-alpha blob 1, located in the southern constellation of Aquarius, some 11.5 billion light-years from Earth.

Stretching three times larger than our own Milky Way galaxy, this thing is ginormous and extremely green, but to this day, no one can say what's illuminating it.

Scientists have suggested that supermassive black holes swallowing matter in galaxies within the central region of the blob could be responsible, and now the team behind this new discovery suspect the same thing is happening to the MAMMOTH-1 nebula.

The MAMMOTH-1 nebula was found by a survey called Mapping the Most Massive Over densities Through Hydrogen (MAMMOTH), which was also responsible for finding the Slug Nebula back in 2014.

The protocluster it's found in is massive, hosting an unusually high concentration of galaxies in an area of about 50 million light-years across - all bound together by gravity.

While the galaxies are now mature, our telescopes are only just seeing them as they would have looked a mere 3 billion years after the Big Bang - the peak of galaxy formation in our Universe.

Several hypotheses have been put forward for how the MAMMOTH-1 nebula at the heart of this great protocluster got so bright, but the most likely ones revolve around radiation or discharges coming from something called an active galactic nucleus (AGN).

AGNs are compact regions at the centre of galaxies that have a much higher than normal luminosity. The team explains that AGNs are powered by a supermassive black hole actively feeding on gas in the centre of a galaxy, and are known for being extremely bright sources of light.

The intense radiation emitted by AGNs ionise the hydrogen gas in the space around it, and this could prompt the ELANs to emit super-bright Lyman-alpha radiation.

Quasars - the brightest objects in the Universe - are known for being the most luminous AGNs in visible light, except the MAMMOTH-1 nebula is not associated with a quasar, as far as the researchers can tell.

But that doesn't mean there isn't one lurking in the background.

"It has all the hallmarks of an AGN, but we don't see anything in our optical images. I expect there's a quasar that is so obscured by dust that most of its light is hidden," Prochaska says.

The team has its work cut out for it in trying to spot a single quasar some 10 billion light-years from Earth, and until then, the brightest known ELAN will remain a cosmic mystery.

The research has been accepted for publication in the Astrophysical Journal, and you can read it in full at the pre-print website, arXiv.org.

What Cassini's Daring Ring-Dive Around Saturn Could Tell Us About Uranus

Ashampoo_Snap_2017.03.02_02h17m12s_001_Glowing in pale blue, Uranus looks like a ghostly planet in pictures taken from the only spacecraft to ever visit it: Voyager 2. Due to the planet's great distance from Earth, follow-up studies of the planet began only in the late 1990s when telescope optics improved. Since then, Uranus has remained a low priority for observational institutions.

That's unfortunate for scientists looking to learn more about the faint rings of Uranus, discovered 40 years ago this year. Two airborne campaigns were set up to watch Uranus pass in front of a star in 1977. And both were taken aback when they found rings circling the planet. One of the teams missed three of the rings because they were so surprised by the find.

There are hopes that a spacecraft will fly to Uranus or Neptune in the 2020s or 2030s. NASA is undertaking early-stage feasibility studies. So it will remain to the plucky Cassini spacecraft, in orbit around Saturn since 2004, to show scientists what it can about the rings of Uranus by analogy with Saturn.

"At the time of the Uranian discovery, we had never seen narrow, dense rings before," said Mark Showalter, a planetary astronomer at the Search for Extra terrestrial Intelligence Institute. "The narrow rings of Saturn behave similarly to the rings of Uranus," he added, "so that has enabled us to understand dense rings a little bit better."

Cassini is in the final year of its epic mission, and is taking a rare close look at Saturn's rings in the coming weeks. The spacecraft is in the midst of performing 20 "ring-grazing orbits" that will allow for the best views of them since Cassini's arrival in 2004. The manoeuvres began in November and run through April.

"[W]e expect to see the rings, along with the small moons and other structures embedded in them, as never before," Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in California, said in a statement. "The last time we got this close to the rings was during arrival at Saturn in 2004, and we saw only their backlit side. Now we have dozens of opportunities to examine their structure at extremely high resolution on both sides."

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Following completion of the ring orbits, Cassini will perform unprecedented dives between Saturn and its rings between April and September. Then, on September 15, Cassini will make a suicidal plunge into Saturn itself to protect icy worlds like Enceladus from the small chance of Cassini crashing into and contaminating their surfaces.

But before that, Showalter points out, Cassini will provide more insights on what is happening within the Uranus system, even though the spacecraft is surveying a completely different planet. The wobbles in Saturn's narrow rings appear to move in similar ways that Uranian rings do, for example.

But there are still several mysteries that may take another Uranian mission to resolve.

For example, images from Voyager 2 depicted dust rings surrounding the main ring system of. Then, when Uranus reached its equinox (closest point in its orbit) in 2008, observations from the Keck Telescope imaged the rings when they were edge-on from Earth, making it easier to identify the presence of any dust. It appears that the dust has shifted 3,100 miles between the two observations, Showalter said. The reason for the shift remains poorly understood.

Another open question is the role that the moons Cornelia and Ophelia play in shepherding the outer ring of Uranus — a phenomena also seen around Saturn. But the rings around Uranus are more difficult to observe right now because the planet is in an area of the sky with fewer stars, Showalter said, meaning the planet remains obscure more than it did in the 1970s and 1980s.

Showalter has been very busy in the past few years working on both the New Horizons mission, which passed by Pluto in 2015, as well as Cassini. He says he hopes to pull out some older data on Uranus soon to learn more about the planet's ring system, and to provide some insight for whenever a spacecraft does visit the Blue World again.