Milky Way grew by ‘cannibalising’ other smaller galaxies

Astronomers using NASA’s Hubble Space Telescope have uncovered tantalising evidence for the possible existence of a shell of stars that are a relic of the Milky Way’s past cannibalism of other galaxies.

Peering deep into the vast stellar halo that envelops our Milky Way galaxy, a team of astronomers led by Alis Deason, from UC Santa Cruz, used Hubble observations to precisely measure, for the first time ever, the sideways motions of a small sample of stars located far from the galaxy’s center.

Their unusual lateral motion is circumstantial evidence that the stars may be the remnants of a shredded galaxy that was gravitationally ripped apart by the Milky Way billions of years ago. These stars support the idea that the Milky Way grew through the accretion of smaller galaxies.

“Hubble’s unique capabilities are allowing astronomers to uncover clues to the galaxy’s remote past,” said coauthor Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore.

“The more distant regions of the galaxy have evolved more slowly than the inner sections. Objects in the outer regions still bear the signatures of events that happened long ago,” Marel said in a statement.

They also offer a new opportunity for measuring the “hidden” mass of our galaxy, which is in the form of dark matter — an invisible form of matter that does not emit or reflect radiation.

“Our ability now to measure the motions of these stars opens up a whole new territory we haven’t explored yet,” Deason said.

Deason and her team plucked the outer halo stars out of seven years’ worth of archival Hubble telescope observations of our neighbouring Andromeda galaxy.

In those observations, Hubble peered through the Milky Way’s halo to study the Andromeda stars, which are more than 20 times farther away.

The Milky Way’s halo stars were in the foreground and considered as clutter for the study of Andromeda. But to Deason’s study they were pure gold.

The observations offered a unique opportunity to look at the motion of Milky Way halo stars.

“We knew these stars were there, because for the Andromeda study we had to separate the stars in Andromeda from the stars in the Milky Way,” said co-author Puragra Guhathakurta, professor of astronomy and astrophysics at UC Santa Cruz.

Researchers said finding the stars was meticulous work. Each Hubble image contained more than 100,000 stars.

“We had to somehow find those few stars that actually belonged to the Milky Way halo. It was like finding needles in a haystack,” Marel said.

Source: http://www.indianexpress.com/news/milky-way-grew-by-cannibalising-other-smaller-galaxies/1078215/0

Tiniest planet ever discovered outside our solar system

NASA has discovered the smallest known planet outside our solar system which is slightly larger than the Moon and orbits its Sun like host star every 13 days.

NASA’s Kepler space telescope detected the smallest planet yet found around a star similar to the Sun in a new planetary system. The planets are located in a system called Kepler-37, about 210 light-years from Earth in the constellation Lyra.

The smallest planet, Kepler-37b, is slightly larger than our Moon, measuring about one-third the size of Earth. It is smaller than Mercury, which made its detection a challenge.

The Moon-size planet and its two companion planets were found by scientists with NASA’s Kepler mission to find Earth-sized planets in or near the “habitable zone,” the region in a planetary system where liquid water might exist on the surface of an orbiting planet.

However, while the star in Kepler-37 may be similar to our Sun, the system appears quite unlike the solar system in which we live.

Astronomers think Kepler-37b does not have an atmosphere and cannot support life as we know it. The tiny planet almost certainly is rocky in composition.

Kepler-37c, the closer neighbouring planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the farther planet, is twice the size of Earth.

“Even Kepler can only detect such a tiny world around the brightest stars it observes,” said Jack Lissauer, a planetary scientist at NASA’s Ames Research Center in Moffett Field, California.

“The fact we’ve discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyse additional data,” said Lissauer in a NASA statement.

Kepler-37’s host star belongs to the same class as our Sun, although it is slightly cooler and smaller. All three planets orbit the star at less than the distance Mercury is to the Sun, suggesting they are very hot, inhospitable worlds.

The estimated surface temperature of this smoldering planet, at more than 800 degrees Fahrenheit, would be hot enough to melt the zinc in a penny. Kepler-37c and Kepler-37d, orbit every 21 days and 40 days, respectively.

We uncovered a planet smaller than any in our solar system orbiting one of the few stars that is both bright and quiet, where signal detection was possible,” said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, California, and lead author of the new study published in the journal Nature.

“This discovery shows close-in planets can be smaller, aswell as much larger, than planets orbiting our Sun,” he said.

Source: http://www.indianexpress.com/news/tiniest-planet-ever-discovered-outside-our-solar-system/1077692/0

NASA’s new mission to estimate impact of asteroids on Earth

NASA plans to launch a new mission in 2016 to find potentially hazardous asteroids and predict their impact threat to Earth.

NASA’s OSIRIS-REx asteroid sample return mission will arrive at RQ36 in 2018 and orbit the asteroid until 2021. By communicating continuously with a spacecraft in orbit around RQ36, the team will get a much better idea of the asteroid’s orbit.

“We expect OSIRIS-REx will enable us to make an estimate of the Yarkovsky force on RQ36 at least twice as precise as what’s available now,” says Jason Dworkin, OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center in Greenbelt.

The Yarkovsky effect happens simply because it takes time for things to heat up and cool down. Objects tend to be coldest just before dawn and warmest at mid-afternoon, after hours of illumination by the high Sun.

The team will use what it learns about the Yarkovsky effect on RQ36 to help estimate the effects on other asteroids, NASA said in a statement.

The key to all these strategies is to discover the asteroid well in advance of its impact date and attempt to deflect it early, according to Edward Beshore of the University of Arizona, Tucson, deputy principal investigator for OSIRIS-REx asteroid sample return mission.

One of the first things that would be done if an asteroid appeared to be on a collision course with Earth is to send a probe to the asteroid that might look very much like OSIRIS-REx, said Beshore.

OSIRIS-REx will determine if RQ36 is actually a rubble pile by orbiting it and revealing the subtle effects on the orbit from the gravity of any large and dense lumps within the asteroid.

A probe like OSIRIS-REx could map the internal structure of an asteroid this way, providing valuable information on where to target the deflection mechanism.

OSIRIS-REx will also determine the composition of RQ36 using remote measurements from both visible light and infrared spectrometers, and by collecting a sample of material from the asteroid’s surface and returning it to Earth for study.

Since the Yarkovsky effect may vary depending on the type of material and its distribution, a probe with OSIRIS-REx’s capability to map the surface composition will enable a more precise estimate of the effect on the asteroid’s orbit.

The mission will also provide critical experience navigating around asteroids.

According to NASA’s Near-Earth Object (NEO) programme, there are more than 1,300 “Potentially Hazardous Asteroids” (PHAs) ¿ objects at least 150 yards across with a very small chance of impacting us someday because their orbital paths take them close to Earth’s orbit.

Source:http://www.indianexpress.com/news/nasas-new-mission-to-estimate-impact-of-asteroids-on-earth/1071471/0