Australian Student Uncovers the Universe’s Missing Mass

Not since the work of Fritz Zwicky has the astronomy world been so excited about the missing mass of the Universe. His evidence came from the orbital velocities of galaxies in clusters, rotational speeds, and gravitational lensing of background objects. Now there’s even more evidence that Zwicky was right as Australian student – Amelia Fraser-McKelvie – made another breakthrough in the world of astrophysics.
Working with a team at the Monash School of Physics, the 22-year-old undergraduate Aerospace Engineering/Science student conducted a targeted X-ray search for the hidden matter and within just three months made a very exciting discovery. Astrophysicists predicted the mass would be low in density, but high in temperature – approximately one million degrees Celsius. According to theory, the matter should have been observable at X-ray wavelengths and Amelia Fraser-McKelvie’s discovery has proved the prediction to be correct.

Dr Kevin Pimbblet from the School of Astrophysics explains: “It was thought from a theoretical viewpoint that there should be about double the amount of matter in the local Universe compared to what was observed. It was predicted that the majority of this missing mass should be located in large-scale cosmic structures called filaments – a bit like thick shoelaces.”


Up until this point in time, theories were based solely on numerical models, so Fraser-McKelvie’s observations represent a true break-through in determining just how much of this mass is caught in filamentary structure. “Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density.” says Amelia. “We examine if a filament’s membership to a supercluster leads to an enhanced electron density as reported by Kull & Bohringer (1999). We suggest it remains unclear if supercluster membership causes such an enhancement.”
Still a year away from undertaking her Honors year (which she will complete under the supervision of Dr Pimbblet), Ms Fraser-McKelvie is being hailed as one of Australia’s most exciting young students… and we can see why!

New Arm Embraces Milky Way

Some sixteen decades ago, Lord Rosse was the first to point out spiral structure in distant “nebula”… and today astrophysicists Thomas Dame and Patrick Thaddeus are discovering it closer to home. Our Milky Way Galaxy was believed to only have six spiral arms, but their research has revealed an outer extension of the Scutum-Centaurus arm from the inner galaxy.

“We have identified a spiral arm lying beyond the Outer Arm in the first Galactic quadrant ~15 kpc from the Galactic center.” says Dame and Thaddeus. “One of the detections was fully mapped to reveal a large molecular cloud with a radius of 47 pc and a molecular mass of ~50,000 M. At a mean distance of 21 kpc, the molecular gas in this arm is the most distant yet detected in the Milky Way.

The new arm appears to be the continuation of the Scutum–Centaurus Arm in the outer Galaxy, as a symmetric counterpart of the nearby Perseus Arm.”

Over the last 50 years, many models of our galaxy have been proposed – revealing a pleasing, duo-symmetry. However, finding evidence to prove these theories has been a bit more elusive. Since we cannot observe ourselves, seeing spiral structure on the far side of the galaxy is problematic – hidden by near-side emission at the same velocity. But these researchers didn’t stop. The new arm was found as a result of attempts to follow the Sct–Cen Arm past its tangent.

“The new arm was largely overlooked in existing 21 cm surveys probably because it lies mainly out of the Galactic plane, its Galactic latitude steadily increasing with longitude as it follows the warp in the distant outer Galaxy.” says Dame. “In the first quadrant the only prominent HI spiral feature in the outer Galaxy is the well-known Outer Arm, a feature also well traced by CO. However, at 3 degrees above the plane one sees instead the new arm as a prominent linear feature running roughly parallel to the locus of the Outer Arm but shifted to more negative velocities.”

Is our smoothly constructed galaxy indeed a mirror image of itself? This new evidence suggests the Scutum-Centaurus arm embraces the entire Milky Way – forming a symmetrical, star-forming counterpart to the galaxy’s other arm, Perseus. “Confirmation of the present feature as the ”Outer Sct-Cen Arm” will require a great deal of new data from several telescopes and much observing time over an extended period.” says Thaddeus. “Key steps toward confirming the proposal include, as mentioned, tracking Sct–Cen in the fourth quadrant and, even harder, tracking the Perseus Arm from the point where it passes inside the solar circle near longitude 50 degrees to its putative origin at the far end of the bar.”

Mapping the findings of galactic data on atomic hydrogen gas isn’t going to happen overnight… and even more discoveries and clarifications could be revealed in the future. “The Galactic symmetry suggested by the present work and clearly demonstrated by the identification of the Far 3-kpc Arm a few years ago, coupled with evidence for a global two-armed spiral pattern in the old stars, and, indeed, with the discovery of the bar itself, all hint at Galactic spiral structure that is both simpler and more amenable to study than had long been assumed. As emphasized here, much work remains, but aided by greatly improved distances from forthcoming astrometric surveys, a reasonably complete picture of our Galaxy’s spiral pattern may be achieved over the next decade.”

GSAT 8 Successful Launch from French Guiana - ISRO

Today India's advanced communication satellite, GSAT-8, was successfully launched at 02:08 hrs IST today (May 21, 2011) by the Ariane-V launch vehicle of Arianespace from Kourou. French Guiana.

Ariane V placed GSAT-8 into the intended Geosynchronous Transfer Orbit (GTO) of 35,861 km apogee and 258 km perigee, with an orbital inclination of 2.503 deg with respect to equator.

ISRO's Facility takes control of the Satellite :
ISRO's Master Control Facility (MCF) at Hassan in Karnataka acquired the signals from GSAT-8 satellite immediately after the injection. Initial checks on the satellite have indicated normal health of the satellite. The satellite was captured in three-axis stabilization mode. 

What Next ?
Preparations are underway for the firing of 440 Newton Liquid Apogee Motor (LAM) during the third orbit of the satellite on May 22, 2011 at 03:58 hrs IST as a first step towards taking the satellite to its geostationary orbital home

Basically there are two main payload in this mission :-
1. Communication Payload:
24 Ku-band transponders each with 36 MHz usable bandwidth employing 140 WTWTAs in order to cover entire Indian mainland including Andaman Nicobar has been placed.

2. Navigation Payload :
Two-channel GAGAN payload operating in LI and L5 bands provides Satellite-based Navigation services with accuracy and integrity required for civil aviation applications over Indian Air Space.