~2 million light-yearsM31 compared with angular
size of Earth’s MoonPlutoNumber discoveredYears2251 1723785732002004006008001930–341935–391940–441945–491950–541955–591960–641965–691970–741975–791980–841985–891990–94 1995–992000–042005–092010–FAST
FAC TASTRONEWS
WWW.ASTRONOMY.COM 19BALANCING ACT. Rosetta has seen a 100-foot-wide (30 meters) boul-
der on Comet 67P/Churyumov-Gerasimenko balancing on a narrow rim.The massive and nearby Andromeda Galaxy (M31)
has a halo even bigger than astronomers thought,
about six times larger and 1,000 times more mas-
sive. This halo of gas is diffuse yet so large that it
contains the mass of half the stars in the galaxy.
Scientists used the Hubble Space Telescope
to study how the nearly invisible gas of the halo
blocks light from background quasars, more dis-
tant galaxies that shine brightly as gas falls into
their central black holes. Normally, these types
of studies can use only one quasar per galaxy,
but the close proximity of M31 means this galaxy
sprawls across a length of sky six times wider than
the size of the Full Moon, allowing astronomersto use 18 quasars in this case and giving them
unprecedented accuracy.
Scientists have known for a while now that
Andromeda and the Milky Way are on a collision
course, speeding toward each other through
the 2.5 million light-years that currently separate
them. The new measurements for Andromeda’s
halo mean our large neighbor actually extends
nearly halfway across that distance already. The
halos of the two galaxies will begin to interact
much sooner than the 4-billion-year count-
down until their stellar populations begin to
merge. The study was published May 10 in The
Astrophysical Journal. — K. H.Andromeda gets a lot bigger
THE SOLAR SYSTEM BEYOND NEPTUNE
TRANS-NEPTUNIAN OBJECTS. When Clyde Tombaugh discovered Pluto in 1930, scientists thought they
had found a missing planet. This distant world remained the only known non-comet beyond Neptune until David
Jewitt and Jane Luu found 1992 QB 1 62 years later. By the end of 2014, astronomers had detected more than
1,500 trans-Neptunian objects, loosely defined as bodies whose average distance from the Sun is greater than
Neptune’s. Much of the apparent drop-off in recent discoveries stems from search teams that don’t report new
finds until they observe an object at multiple appearances. ASTRONOMY: RICHARD TALCOTT AND ROEN KELLYThe two largest trans-Neptunian
objects found to date are Pluto and
Eris. Pluto measures about 1,485 miles
(2,390 kilometers) in diameter and Eris
is some 40 miles (64km) smaller.HUGE HALO. Hubble
viewed distant, bright
objects called quasars to
determine the extent of
the Andromeda Galaxy’s
halo. If they saw a dip in
the quasar’s light at cer-
tain wavelengths, they
could tell they were peer-
ing through the fuzz of
the halo. NASA/ESA/A. FEILD (STSCI)zŽƵŚĂǀĞŶΖƚďĞĞŶƵŶĚĞƌƚŚĞ
͚DŝůŬLJtĂLJ͛ƵŶƟůLJŽƵŚĂǀĞ
ďĞĞŶ͚ŽǁŶhŶĚĞƌ͛͘͘͘
,ŽŵĞŽĨƚŚĞŝŐŐĞƐƚWƵďůŝĐ
dĞůĞƐĐŽƉĞŽŶƚŚĞWůĂŶĞƚdŚĞDŝůƌŽLJκϬŝŶĐŚ͘
Invites
Astro-photographers
and Astro-Tourists to the
Worlds First Astronomy Resort Use the Best Telescope
Under the Best Dark Skies
/Ŷ>ƵdžƵƌLJĐĐŽŵŵŽĚĂƟŽŶAustralia
http://www.milroyobservatory.com.au
[email protected]
phone Aust +61 448 129 119