29 May 2017

China's space telescope to observe 'big eaters' in universe

20170529144851CHINA'S new space telescope to be launched soon will probe many mysteries of the universe, including the belching "big eaters" -- active galactic nuclei at the most remote edges of the universe.

Scientists have discovered that almost every galaxy has a supermassive black hole with a mass several million to several billion times that of the Sun at its centre. With their mighty gravitational attraction, the supermassive black holes engulf the surrounding gas and dust.

When a black hole swallows too much, the excess matter is converted into two jet-flows perpendicular to the accretion disk of the black hole, which is like a glutton with a bloated belly belching.

The jet-flows and accretion disk of the supermassive black hole generate X-ray radiation strong enough to travel billions of light years. These galaxies have very bright nuclei -- so bright the central region can be more luminous than the remaining galaxy. Scientists call them active galactic nuclei.

The Hard X-ray Modulation Telescope (HXMT), developed by Chinese scientists, will observe some active galactic nuclei.

"Since the active galactic nuclei are very far from the Earth, our telescope can only detect the brightest ones," says Zhang Shuangnan, lead scientist of HXMT and director of the Key Laboratory of Particle Astrophysics at the Chinese Academy of Sciences (CAS).

The big eaters are full of mysteries. Scientists have found the double jet phenomenon is very common in galaxies with active galactic nuclei, but they don't understand why supermassive black holes cannot engulf all the matter falling into them.

Supermassive black holes are very different from black holes of stellar mass, which are formed when very massive stars collapse at the end of their life cycles. Scientists are still not clear how supermassive black holes are formed and grow, which is a key to understanding the evolution of galaxies.

HXMT's observation is expected to help scientists see the core region close to the event horizon of supermassive black holes at the centre of active galaxies and gather information about the extremely strong gravitational fields, Zhang says.


28 May 2017

China's space telescope to survey Milky Way

CoEs42PWEAA979FMany black holes and neutron stars are thought to be hidden in the Milky Way. Since they don't emit visible light, or are covered by dust, only X-ray telescopes can find them.

China will soon launch its first X-ray space telescope, the Hard X-ray Modulation Telescope (HXMT), with the aim of surveying the Milky Way to observe celestial sources of X-rays.

"Our space telescope has unique capabilities to observe high-energy celestial bodies such as black holes and neutron stars. We hope to use it to resolve mysteries such as the evolution of black holes and the strong magnetic fields of neutron stars," says Zhang Shuangnan, lead scientist of HXMT and director of the Key Laboratory of Particle Astrophysics at the Chinese Academy of Sciences (CAS).

"We are looking forward to discovering new activities of black holes and studying the state of neutron stars under extreme gravity and density conditions, and the physical laws under extreme magnetic fields. These studies are expected to bring new breakthroughs in physics," says Zhang.

Compared with X-ray astronomical satellites of other countries, HXMT has larger detection area, broader energy range and wider field of view. These give it advantages in observing black holes and neutron stars emitting bright X-rays, and it can more efficiently scan the galaxy, Zhang says.

The telescope will work on wide energy range from 1 to 250 keV, enabling it to complete many observation tasks previously requiring several satellites, according to Zhang.

Other satellites have already conducted sky surveys, and found many celestial sources of X-rays. However, the sources are often variable, and occasional intense flares can be missed in just one or two surveys, Zhang says.

New surveys can discover either new X-ray sources or new activities in known sources. So HXMT will repeatedly scan the Milky Way for active and variable celestial bodies emitting X-rays.

Cpk5ENWXgAYevMTZhang says other countries have launched about 10 X-ray satellites, but they have different advantages and therefore different observation focuses.

"There are so many black holes and neutron stars in the universe, but we don't have a thorough understanding of any of them. So we need new satellites to observe more," Zhang says.

The study of black holes and neutron stars is often conducted through observing X-ray binary systems. The X-ray emissions of these binary systems are the result of the compact object (such as black hole or neutron star) accreting matter from a companion regular star.

By analysing binary system X-ray radiation, astronomers can study compact objects such as black holes or neutrons stars.

How do the black holes or neutron stars accrete matter from companion stars? What causes X-ray flares? These are questions scientists want to answer, and China's new space telescope might help.

Lu Fangjun, chief designer of the payload of HXMT, says the space telescope will focus on the Galactic plane. If it finds any celestial body in a state of explosion, it will conduct high-precision pointed observation and joint multiband observation with other telescopes either in space or on the ground.

26 May 2017

There are more black holes in the Universe than previously thought

Ashampoo_Snap_2017.05.26_09h17m13s_002_Astronomers have found what looks to a fresh trove of supermassive black hole pairs, increasing the number of known pairs by about 50 percent, after new image analysis techniques were used to study two of our most detailed sky surveys.

Finding these black hole pairs is crucial to understanding more about how they form and how galaxies eventually collide, with the new findings giving astronomers five new pairs to analyse.

At the centre of the new research is the hunt for dual active galactic nuclei (AGN) - the technical term for what's formed when two supermassive black holes get caught in a death spiral after the collision of their respective galaxies.

These two black holes get closer and closer before eventually crashing into each other to form an even larger supermassive black hole, shooting out huge amounts of energy at the same time - or at least that's the current hypothesis.

Occasionally, the collision seems to send the resulting black hole speeding off through space, but that's another story.

The AGNs are formed from the massive amounts of gas and dust stirred up as a result of this black hole death spiral, causing the final, really supermassive black hole to be heavier.

Active galactic nuclei can form around any black hole, giving us a better chance of spotting them from Earth, but to understand how all this works, we need to find more of them.

"Our model of the universe tells us [AGNs] should be there, but we have failed miserably to find them," lead research Sara Ellison from the University of Victoria in Canada told New Scientist.

Ellison and her colleagues looked at the WISE All Sky Survey and the Sloan Digital Sky Survey for their work, hunting for signs of recent galaxy collisions as well as high readings from the infrared part of the spectrum, which indicates lots of dust.

Further confirmation was found from luminosity measurements taken by the Chandra X-ray Observatory. The new technique turned up five new examples of dual AGNs, to add to the nine that had already been confirmed by X-ray studies.

That's "a significant new haul", write the researchers, and there could be more on the way.

We should point out that the research has yet to go through the peer-review process, so further confirmation of the findings is needed before they're confirmed, but this could end up being a very useful way of detecting more of these AGNs.

Once astronomers know where they are, they can study how they evolve, and how the resulting supermassive black holes grow.

These AGNs could also teach us more about gravitational waves, another after-effect of a collision of two black holes: or at least they will when the shock reaches us, in tens of millions of years.

25 May 2017

A Whole New Jupiter: First Science Results from NASA's Juno Mission

ThumbEarly science results from NASA's Juno mission to Jupiter portray the largest planet in our solar system as a complex, gigantic, turbulent world, with Earth-sized polar cyclones, plunging storm systems that travel deep into the heart of the gas giant, and a mammoth, lumpy magnetic field that may indicate it was generated closer to the planet's surface than previously thought.

"We are excited to share these early discoveries, which help us better understand what makes Jupiter so fascinating," said Diane Brown, Juno program executive at NASA Headquarters in Washington. "It was a long trip to get to Jupiter, but these first results already demonstrate it was well worth the journey."

Juno launched on Aug. 5, 2011, entering Jupiter's orbit on July 4, 2016. The findings from the first data-collection pass, which flew within about 2,600 miles (4,200 kilometers) of Jupiter's swirling cloud tops on Aug. 27, are being published this week in two papers in the journal Science, as well as 44 papers in Geophysical Research Letters.

"We knew, going in, that Jupiter would throw us some curves," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. "But now that we are here we are finding that Jupiter can throw the heat, as well as knuckleballs and sliders. There is so much going on here that we didn't expect that we have had to take a step back and begin to rethink of this as a whole new Jupiter."

Among the findings that challenge assumptions are those provided by Juno's imager, JunoCam. The images show both of Jupiter's poles are covered in Earth-sized swirling storms that are densely clustered and rubbing together.

"We're puzzled as to how they could be formed, how stable the configuration is, and why Jupiter's north pole doesn't look like the south pole," said Bolton. "We're questioning whether this is a dynamic system, and are we seeing just one stage, and over the next year, we're going to watch it disappear, or is this a stable configuration and these storms are circulating around one another?"

Another surprise comes from Juno's Microwave Radiometer (MWR), which samples the thermal microwave radiation from Jupiter's atmosphere, from the top of the ammonia clouds to deep within its atmosphere. The MWR data indicates that Jupiter's iconic belts and zones are mysterious, with the belt near the equator penetrating all the way down, while the belts and zones at other latitudes seem to evolve to other structures. The data suggest the ammonia is quite variable and continues to increase as far down as we can see with MWR, which is a few hundred miles or kilometres. 

Prior to the Juno mission, it was known that Jupiter had the most intense magnetic field in the solar system. Measurements of the massive planet's magnetosphere, from Juno's magnetometer investigation (MAG), indicate that Jupiter's magnetic field is even stronger than models expected, and more irregular in shape. MAG data indicates the magnetic field greatly exceeded expectations at 7.766 Gauss, about 10 times stronger than the strongest magnetic field found on Earth.

"Juno is giving us a view of the magnetic field close to Jupiter that we've never had before," said Jack Connerney, Juno deputy principal investigator and the lead for the mission's magnetic field investigation at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Already we see that the magnetic field looks lumpy: it is stronger in some places and weaker in others. This uneven distribution suggests that the field might be generated by dynamo action closer to the surface, above the layer of metallic hydrogen. Every flyby we execute gets us closer to determining where and how Jupiter's dynamo works."

Juno also is designed to study the polar magnetosphere and the origin of Jupiter's powerful auroras -- its northern and southern lights. These auroral emissions are caused by particles that pick up energy, slamming into atmospheric molecules. Juno's initial observations indicate that the process seems to work differently at Jupiter than at Earth.

Juno is in a polar orbit around Jupiter, and the majority of each orbit is spent well away from the gas giant. But, once every 53 days, its trajectory approaches Jupiter from above its north pole, where it begins a two-hour transit (from pole to pole) flying north to south with its eight science instruments collecting data and its JunoCam public outreach camera snapping pictures. The download of six megabytes of data collected during the transit can take 1.5 days.

"Every 53 days, we go screaming by Jupiter, get doused by a fire hose of Jovian science, and there is always something new," said Bolton. "On our next flyby on July 11, we will fly directly over one of the most iconic features in the entire solar system -- one that every school kid knows -- Jupiter's Great Red Spot. If anybody is going to get to the bottom of what is going on below those mammoth swirling crimson cloud tops, it's Juno and her cloud-piercing science instruments."

NASA's Jet Propulsion Laboratory in Pasadena, California, manages the Juno mission for NASA. The principal investigator is Scott Bolton of the Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, for the agency's Science Mission Directorate. Lockheed Martin Space Systems, in Denver, built the spacecraft.

21 May 2017

Rainfall on Mars shaped the planet

MARS_Helmets_DLAt one stage in its history rain storms on Mars were so heavy – and the raindrops so large – that they changed the planet’s surface, carving valleys and altering the shape of meteorite impact craters, new research shows.

A paper by geologists Robert Craddock and Ralph Lorenz, published in the journal Icarus, suggests that over billions of years Mars’s atmospheric pressure fell, powering up the nature of its rainfall.

Soon after its formation around 4.5 billion years ago, atmospheric pressure on the red planet was around four bars. To compare, Earth’s is one.

At that pressure, Craddock and Lorenz say, rain would have looked more like mist. Raindrops could not have grown to more than three millimetres in diameter, and would not have penetrated the ground when they hit it.

Over deep time, however, the atmospheric pressure decreased to around 1.5 bars. This, combined with lower gravity than that of Earth, meant that raindrops as large as 7.3 millimetres across could form – substantially bigger than the 6.5 millimetre whoppers sometimes recorded on our own planet.

The geologists calculate that the intensity of big falls would have been only about 70% of those found on Earth, but would still have been easily strong enough to put a dent or two in the ground.

Indeed, they suggest that the falls would have overwhelmed the soil’s ability to absorb moisture, thus creating run-off currents that eventually formed valley networks and reshaped impact craters.

“We have shown that Mars would have seen some pretty big raindrops that would have been able to make more drastic changes to the surface,” comments Lorenz, from Johns Hopkins University in the US.

Craddock, who works at the Smithsonian Institute, adds that their paper represents the first time scientists have used physics to gain insight into the Martian climate.

“There will always be some unknowns, of course, such as how high a storm cloud may have risen into the Martian atmosphere, but we made efforts to apply the range of published variables for rainfall on Earth,” he adds.

“It’s unlikely that rainfall on early Mars would have been dramatically different than what's described in our paper.”

9 May 2017

scientists now want to send a space probe to orbit Pluto

Pluto-01_Stern_03_Pluto_Color_TXTHumanity's first up-close look at Pluto was so intriguing that some researchers want to go back and spend a lot more time studying the icy world.

Late last month, 35 scientists met for 7 hours in Houston to discuss the basic blueprint and science goals of a potential Pluto orbiter mission. Such an effort would build upon the knowledge gained during the epic Pluto flyby performed in July 2015 by NASA's New Horizons probe.

Participants came away from the April 24 workshop fired up and committed to doing their best to make such a project happen, said New Horizons principal investigator Alan Stern, who was there. [Destination Pluto: NASA's New Horizons Mission in Pictures]

The meeting was reminiscent, Stern said, of New Horizons' earliest days: the late 1980s, when he and a few other people first raised the possibility of launching a flyby mission to Pluto.

"It felt a lot like that, but [with] a new generation of people," Stern, who's based at the Southwest Research Institute in Boulder, Colorado, told Space.com.

New Horizons' flyby revealed Pluto to be a stunningly diverse world with vast plains of nitrogen ice, 2-mile-high (3.2 kilometers) mountains of water ice and a wealth of other surface features. But the probe got just a fleeting look at the dwarf planet system while zooming by; an orbiter would linger and lift Pluto's veil even more, Stern said.

"You could map every square inch of the planet and its moons," he said. "It would be a scientific spectacular."

As the possible mission is currently envisioned, the orbiter would cruise around the Pluto system, using gravity assists from the dwarf planet's largest moon, Charon, to slingshot it here and there, Stern said. The strategy would be similar to that employed by NASA's Cassini spacecraft, which has shaped its path through the Saturn system over the years via flybys of the ringed planet's largest moon, Titan.

The current concept is therefore different from one Stern proposed shortly after New Horizons' flyby, which would have put a lander down on Charon.

With a Charon lander, "you're stuck looking at one side of Pluto," Stern said. (Charon and Pluto are tidally locked, meaning each world always shows the same face to the other.)


"And you can't get in superclose. You can't get down in the atmosphere," he added. "This, I think, is a better mission concept."

Though the mission would be Cassini-like, the Pluto orbiter itself would resemble NASA's Dawn probe, which is currently circling the dwarf planet Ceres, Stern said. Like Dawn, the Pluto probe would likely use electric propulsion and have a half-dozen science instruments, he said.

However, because the Pluto orbiter would be operating so far from the sun, it would rely on nuclear power to generate its electricity, rather than sunlight, as Dawn does, Stern added. And the price tag would be higher than Dawn's $467 million; the Pluto effort would probably qualify as a New Frontiers mission or a small flagship. (New Frontiers missions cost about $1 billion, whereas flagships run about $2 billion.)

Stern said a Pluto orbiter could get off the ground in the late 2020s or so. A 2030 launch would have ceremonial significance, coming on the 100th anniversary of Pluto's discovery, he added. The probe would spend seven or eight years journeying to the dwarf planet, then perhaps four or five years studying Pluto and its moons.

When the probe's work there was done, Stern said, the spacecraft could conceivably use one last Charon flyby to escape the Pluto system and head toward another object in the Kuiper Belt, the ring of frigid bodies beyond Neptune's orbit. (New Horizons is doing something similar; it's now headed for a Jan. 1, 2019, flyby of a small Kuiper Belt object called 2014 MU69.)

But a Pluto orbiter mission is a long way from becoming reality, Stern stressed. He said he and his fellow researchers aim to mature the concept in time for it to be considered during the next Planetary Science Decadal Survey, a U.S. National Research Council effort that sets exploration priorities for NASA every 10 years.

The next decadal survey will start in 2020, finish in 2022 and be published in 2023, Stern said.

"The curtain is opening," he said of the Pluto orbiter idea. "This thing is going to be a topic of discussion now for the next few years."