{tab=Celestial cannibals}

Celestial cannibals...

     Cannibalism involves preying on the members of the same species. Certain living beings on Earth are known to practise it. Interestingly, heavens are also not spared from this sordid habit. Astronomers have recently witnessed galaxies which feast on other galaxies. This galactic cannibalism is being watched by astronomers curiously, because it is throwing light on one of the longstanding mysteries in cosmic sciences. This mystery is regarding certain type of spiral galaxies viz. Seyfert galaxies. Cores of these galaxies are very bright. These galaxies are known to host supermassive black holes inside the core. Intense brightness of the core arises from the energy acquired by large quantity of material falling into these black holes. Although the mechanism for this process is known, astronomers did not know wherefrom all this grub comes. Now, Very Large Array Radio Telescope (New Mexico, USA) has shown that the source of this incoming material is none but the nearby galaxies!

Optical (left) and radio (right) images of interacting galaxies
[Credit: NRAO/AUI/NSF]

     Scientists working with Very Large Array Telescope have taken radio-images of different Seyfert galaxies and compared them with their optical counterparts. Although optical images do not reveal any details, radio-images clearly show the inflow of hydrogen gas from the neighbouring galaxies. When these studies advance further, astronomers may be able to describe the conditions in-and-around the Seyfert galaxies more precisely. Cheng-Yu Kuo from University of Virginia, who is involved in this research, recounts this merited discovery saying - "Very Large Array Telescope lifted the veil on what is really happening with these galaxies...!".

{tab=Massive limit}

Massive limit ...

     How massive a star can be at most? Theory restricts the mass of a star to about 150 times that of our Sun. Stars heavier than this are extremely luminous. Exceedingly high population of light photons inside such stars generates tremendous pressure (called radiation pressure) that would disturb the hydrostatic equilibrium inside the star. This pressure would beak apart the star destructively. Astronomers want to establish this limit for mass of a star factually. The heaviest stars discovered so far had masses less than 90 times that of Sun. Now, astronomers have gone one step closer to the theoretical limit with the discovery of a supermassive star weighing as much as 116 solar masses. This discovery was made by a team of researchers from Canada, UK and France.

Open cluster NGC 3603 (at the centre)
[Credit: HST/NASA]

   This 'super heavyweight' star is a member of a binary stellar system revolving around common centre of gravity with a period of 3.77 days. Its companion star is also a superheavy star which is about 89 times heavier than Sun. The binary system dwells in a young (only one million year old) open cluster NGC 3603, lying within the Carina arm of Milky Way Galaxy. These inferences are based on radial velocities of the stars, determined spectroscopically (near-IR) using Very Large Telescope of European Southern Observatory in Chile.

(Above work on massive stars was initially presented in the last year's annual meeting of Canadian Astronomical Society. Recently, the same was submitted to International Astronomical Union in revised form.)

{tab=Predicting a supernova}

Predicting a supernova...

     Scientists know something about what happens to a dying star after it undergoes supernova explosion. But scientists do not know much about what happens to star before this explosion, since the timing of the later cannot be foretold. Now, it may be possible to predict death of a star at least few weeks before it explodes. An international team of scientists could correlate an ultraviolet glow exhibited by a star to a supernova explosion that occurred two weeks after the glow was recorded. Source of both these events was found to be the same red giant star residing in a galaxy about one billion light-years away from us. These recently published results are based on optical and ultraviolet images captured by 3.6 meter Canada-France-Hawaii Telescope and GALEX space telescope in the year 2004.

Host galaxy (composite images): Before brightening (left) and brightened (right)
 [Credit: NASA/HST/COSMOS/GALEX]

     Supernova denotes huge amount of energy that is released when core of a dying star collapses terminally. It involves outward-moving shock wave that leads to the violent expulsion of the outer envelope of a star. Theory suggests that there should be strong heating of the star before the shock wave reaches the surface. This should raise the temperature of the outer layers of the star to 100,000 C. Heating is accompanied by brightening of the star in ultraviolet region. In the present case, brightening of the star had lasted for about six hours. Such ultraviolet brightening may probably be treated as advance intimation of the following stellar explosion. Although it is the first time that such correlation was established, Dr. Kevin Schawinski (U.K.) and other researchers involved in these studies enunciate that - "Dedicated search for similar events is likely to yield more examples." This discovery has shown astronomers a way to observe the final stage in the stellar life-cycle.

{tab=Plutoid Pluto}

Plutoid Pluto...

     Pluto was deprived of its planethood two years ago and now it is considered as a 'dwarf planet'. Now, Pluto has been alleviated to some extent by naming a group of certain dwarf planets after Pluto. Members of this new sub-group will be known as 'plutoids'. This decision was taken in a recent meeting of executive committee of International Astronomical Union held at Oslo, Norway. Conditions to be satisfied by a solar system object for to be qualified as plutoid, can be expressed in simple words as: (1) Object should be beyond Neptune, (2) It should have sufficient self-gravity to impart itself near-spherical shape and (3) Its gravity should not be too strong to capture all the surrounding celestial objects. Satellites of plutoids will not fall into this sub-group.

Plutoids: Pluto (left) and Eris (right) along with their satellites
[Source: NASA/ESA/HST]

     At present, there are only two plutoids known - one is Pluto itself and other is Eris. With semi-major axes of 39.5 A.U. and 67.7 A.U., respectively, both, Pluto and Eris, are farther away from the Sun than Neptune. (Neptune has a semi-major axis of 30.1 A.U.) Both of them have more or less similar diameter of about 2,400 km. But Eris is about 25% more massive than Pluto. Although at present the sub-group consists of only 2 members, astronomers anticipate the expansion of this sub-group in future as a wake of new discoveries.

{tab=Fastest rotating asteroid}

Fastest rotating asteroid...

     Recently discovered ‘2008 HJ’ is a tiny asteroid - just 12 meters by 24 meters in dimensions. But it is not an ordinary asteroid. It is proved to be the fastest-rotating celestial object, known so far, in our solar system. It is rotating around its own axis once in just 42.7 seconds. Previous record holder was asteroid ‘2000 DO8’ with a rotation period of 78 seconds. The newly discovered asteroid completes an orbit around the Sun in about 2 years. When closest, it is at 1 A.U. from the Sun and when farthest, it is at 2.2 A.U. from the Sun. The asteroid is rotating at such a high speed that it cannot gravitationally retain any loose pebble on the surface.

Asteroid 2008 HJ (Seen moving at the centre)
[Credit: Richard Miles/Faulkes Telescope Project]

     The asteroid was discovered by British amateur astronomer Richard Mile on April 24 with 2.0 meter robotic Faulkes Telescope (Australia), seating in his backyard observatory in Dorset (England). This was achieved via internet, under the auspices of Faulkes Telescope Project run for research-based science education. Rotation period of the asteroid was determined from the changes in its brightness during the rotation. The asteroid passed within 3 lunar distances from Earth in the week following its discovery, sailing at a rattling speed of 160,000 km/hour.

{tab=mallest extrasolar planet}

Smallest extrasolar planet...

     Astronomers are looking for smaller and smaller extrasolar planets - especially comparable to our Earth. And they are coming closer and closer to it...! As a latest achievement, an international research team led by David Bennett from University of Notre Dame (USA) was successful in discovering an extrasolar planet which is just 3.3 times heavier than our Earth. This is the smallest extrasolar planet discovered yet. Surprisingly, its parent star is also a lightweight star with a mass equal to only 6% of that of Sun. So far, no planets were known to be tied to any star lighter than 20% of mass of Sun. The planet is revolving around the star at a distance, same as that of Venus from the Sun. The system resides in the constellation of Sagittarius and is 3,000 light years away from us. Planet is expected to have a thick atmosphere and it may be colder than Pluto.

Image of star ‘MOA-2007-BLG-192L’ (Inside the circle)
[Credit: ESO/VLT]

     The planet was discovered using gravitational microlensing technique. If an extrasolar planet passes behind the parent star, the gravitation of the later bends the light-rays coming from the planet. It results in brightening of the image of the planet (as a magnifying lens does). This microlensing effect affects the light-curve of the star in a peculiar way, making the planet perceivable. The same effect contributed to the discovery of this particular planet. Discovery involved the use of 1.8 m telescope of Mt. John Observatory (in New Zealand) and Very Large Telescope of European Southern Observatory (in Chile). The parent star is designated as 'MOA-2007-BLG-192L' and the planet is called with the same name but with a suffix ‘b’ added to it.