blogtecaolivelli

ASTRO.......

fonte: Internet

Astronews a cura di Massimiliano Razzano

• 

  A volte il cielo si tinge di viola e di verde,

  Grazie ad Aurorasaurus è infatti possibile

•  tenere traccia delle posizioni e degli istanti

•  in cui le aurore compaiono. Non sono quelle

•  normali ma anche quelle più curiose e strane

•  come appunto il fenomeno degli STEVE.

•  La NASA ha anche rilasciato un particolare 

• "identikit" di STEVE, che gli appassionati

•  possono utilizzare per scovare questi fenomeni 

• nelle loro fotografie. Capire i processi fisici 

• coinvolti nelle aurore è molto importante anche 

• per studiare come possono influenzare il

•  funzionamento dei satelliti e delle comunicazioni

•  satellitari.

•  con lunghissime strisce che solcano la volta celeste. 

• I primi a vederle sono stati gli appassionati di

•  fotografia, che si sono divertiti a riprendere queste

•  curiose aurore boreali e a dar loro persino un 

• nome simpatico, Steve. La scoperta ha poi attirato

•  l'attenzione degli scienziati della NASA, che hanno

•  iniziato a studiare questi fenomeni assegnando 

• loro il nome di Strong Thermal Emission Velocity 

• Ehnancement, in modo da mantenere la sigla STEVE. 

• Si tratta di un tipo di aurora polare ancora misterioso,

•  e allora la NASA ha chiesto ufficialmente l'aiuto degli

•  appassionati di tutto il mondo tramite, che possono

•  andare a caccia di aurore e segnalarle sul sito 

• Aurorasaurus, un interessante progetto di citizen

•  science dedicato a questi curiosi fenomeni atmosferici.

ASTRO....

fonte: Internet

Astronews a cura di Massimiliano Razzano

• Space Station Sacrifices Progress Module to Dump Trash into Pacific

After all the excitement about last week's successful

docking of the European ATV "Jules Verne", it's time

 to spare a thought for its Russian predecessor.

The Progress 28 module was filled with rubbish

and unneeded equipment, quietly severed from

 its docking bay and steered toward Earth.

 On Monday at 0850 GMT, the selfless module

 dropped through the atmosphere, burned and

 eventually reached the Pacific Ocean, sinking

into the satellite graveyard 3000 km east of the

New Zealand coast...

On February 5th, a Russian Soyuz rocket launched

 the Progress 28 cargo ship to the International Space

 Station (ISS) to ferry supplies to the astronauts in orbit.

This mission started a very busy period for space traffic

 controllers. Soon after Progress 28 was sent on its way,

Space Shuttle Atlantis blasted off to take the 

Columbus module to be installed on the station.

 Then at the start of this month, ESA's Automated Transfer

 Vehicle (ATV) sat patiently in an orbital holding pattern 

until the shuttle undocked and flew back to Earth. Then on

 April 3rd, the ATV carried out a flawless

 approach and docking procedure with the ISS.

Watching over all this action on the station was the

Progress 28 module attached patiently to the Russian

-built Pirs docking compartment. After astronauts had

salvaged reusable parts from the Progress module and

filled it full of trash, the time came on April 7th to say 

Spokojnoj Nochi (Russian for "Good Night") to the ill-fated

 supply ship to make room for the two Russians and one

 South Korean to arrive after the Soyuz launch yesterday.

Dropping supply modules into the Pacific may sound

unsavoury, but it remains the only viable option to dispose

 of rubbish and unwanted material when in space. Simply

 jettisoning it into space cannot be done, there must be a

controlled disposal, dumping trash into a used module and

blasting it into a re-entry trajectory. Littering Earth orbit

 is a critical problem, so space agencies are doing the best

they can to send potential debris to Earth where most of it

can burn up in the atmosphere. Anything left over falls into

a predetermined "satellite graveyard" in the worlds largest ocean.

ASDTRONEWS....

fonte: Internet

Astronews a cura di Massimiliano Razzano

After all the excitement about last week's

successful docking of the European ATV "

Jules Verne", it's time to spare a thought for

its Russian predecessor. The Progress 28

module was filled with rubbish and unneeded

 equipment, quietly severed from its docking

 bay and steered toward Earth. On Monday at 0850

 GMT, the selfless module dropped through the

atmosphere, burned and eventually reached the

Pacific Ocean, sinking into the satellite graveyard 3000 km east of the New Zealand coast...

On February 5th, a Russian Soyuz rocket launched

 the Progress 28 cargo ship to the International

 Space Station (ISS) to ferry supplies to the astronauts

in orbit. This mission started a very busy period for space

 traffic controllers. Soon after Progress 28 was sent on its

way, Space Shuttle Atlantis blasted off to take the

 Columbus module to be installed on the station.

 Then at the start of this month, ESA's Automated Transfer

Vehicle (ATV) sat patiently in an orbital holding pattern 

until the shuttle undocked and flew back to Earth.

Then on April 3rd, the ATV carried out a flawless

 approach and docking procedure with the ISS.

Watching over all this action on the station was the

 Progress 28 module attached patiently to the Russian

-built Pirs docking compartment. After astronauts had

salvaged reusable parts from the Progress module and

 filled it full of trash, the time came on April 7th to say 

Spokojnoj Nochi (Russian for "Good Night") to the ill-

fated supply ship to make room for the two Russians and

one South Korean to arrive after the Soyuz launch yesterday.

Dropping supply modules into the Pacific may sound

unsavoury, but it remains the only viable option to dispose

of rubbish and unwanted material when in space. Simply

 jettisoning it into space cannot be done, there must be a

controlled disposal, dumping trash into a used module and

 blasting it into a re-entry trajectory. Littering Earth orbit is

a critical problem, so space agencies are doing the best they

 can to send potential debris to Earth where most of it can

 burn up in the atmosphere. Anything left over falls into a

 predetermined "satellite graveyard" in the worlds largest ocean.

ASTRONEWS

fonte: Internet

Astronews a cura di Massimiliano Razzano

• What Happens When Three Black Holes Collide?

The consequences of two black holes colliding may be huge,

 the energy produced by such a collision could even be 

detected by observatories here on Earth. Ripples in space-

time will wash over the Universe as gravitational waves

 and are predicted to be detected as they pass through

the Solar System. Taking this idea one step further, what

 would happen if three black holes collide? Sound like science

fiction? Well it's not, and there is observational evidence that

 three black holes can cluster together, possibly colliding after

 some highly complex orbits that can only be calculated by the

 most powerful computers available to researchers...

Back in January 2007, a quasar triplet was observed

 over 10 billion light years away. Quasars are generated

 by the supermassive black holes eating away at the

core of active galaxies. Using the powerful W. M. Keck

Observatory, researchers from Caltech were able to peer

 back in time (10 billion years) to see a period in the

 Universe's life when active galaxies and black hole

 mergers would have been fairly common events

 (when compared to the calmer Universe of today).

They observed three tightly packed quasars, an

unprecedented discovery.

Now, scientists Manuela Campanelli, Carlos Lousto and

Yosef Zlochower, all working at Rochester Institute of

 Technology's Center for Computational Relativity and

Gravitation, have simulated the highly complex mechanisms

behind three interacting and merging supermassive black

holes, much like the situation observed by Keck in 2007.

 The same group have worked on calculating the collision

of two black holes before and have written a code that is

 powerful enough to simulate the collision of up to 22 black

holes. However, 22 black holes probably wouldn't collide

 naturally, this simply demonstrates the stability of the code,

"Twenty-two is not going to happen in reality, but three or

 four can happen," says Yosef Zlochower, an assistant

professor. "We realized that the code itself really didn't

care how many black holes there were. As long as we

could specify where they were located - and had enough

 computer power - we could track them."

These simulations are of paramount importance to the

gravitational wave detectors such as the

 Laser Interferometer Gravitational-Wave Observatory (LIGO).

 So far there has been no firm evidence to come from

these detectors, but more time is needed, the LIGO

 detector requires several years of "exposure time"

to collect enough data and remove observational "noise".

 But what do gravitational wave astronomers look for?

This is the very reason many different cosmic scenarios

 are being simulated so the characteristics of events like

 two or three black holes mergers can be identified from

their gravitational wave signature.

• 09/04/2008 - A Case of MOND Over Dark Matter

Dalle galassie.....

Astronews a cura di Massimiliano Razzano

 A Case of MOND Over Dark Matter According to Newton's

Second Law of Dynamics,

they have lower velocities than objects near the center.

But observations confirm that galaxies rotate

witha uniform velocity. Some astronomers believe the

orbital behavior of galaxies can be explained more

accurately with Modified Newtonian Dynamics (MOND)

a modified version of Newton's Second Law - than by

the rival, but more widely accepted, theory of darkmatter.

The dark matter theory assumes that a halo

of dark matter surrounds each galaxy, providing enough

matter (and gravity) that all the stars in a galaxy disc 

orbit with the same velocity. MOND, however uses a

different explanation, and a recent study of eight dwarf

galaxies that orbit the Milky Way seems to favor the

MOND approach over the dark matter theory.

"MOND was first suggested to account for things that we

see in the distant universe," said Garry Angus, of the

 University of St Andrews. "This is the first detailed study

in which we've been able to test out the theory on something

 close to home. The MOND calculations and the observations

appear to agree amazingly well."

Usually the equation F=ma (force = mass X acceleration)

solves your basic acceleration problems. But it doesn't

explain the observed rotation of galaxies. MOND suggests

that at low values of acceleration, the acceleration of a

particle is not linearly proportional to the force. According

to Angus, MOND adds a new constant of nature (a0) to

physics, besides the speed of light and Planck's constant.

Above the constant, accelerations are exactly as predicted

by Newton's second law (F=ma). Below it, gravity decays

with distance from a mass, rather than distance squared.

This constant is so small that it goes unnoticed with the

large accelerations that we experience in everyday life.

For instance, when we drop a ball the gravity is 100 billion

times stronger than a0 and the accelerated motion of the

Earth round the Sun is 50 million times stronger.

However, when objects are accelerating extremely slowly,

as we observe in galaxies or clusters of galaxies, then the

constant makes a significant difference to the resulting

gravitational forces.

When MOND is applied to nearby dwarf galaxies, one

effect is that tidal forces from the Milky Way, which have

a negligible effect in classical Newtonian Mechanics, can

actually make a big difference. This is particularly significant

for the dwarfs orbiting close to our Galaxy.

"In these dwarf galaxies, the internal gravity is very weak.

Compared to the gravity of the Milky Way," said Angus,

"MOND suggests that the Milky Way is a bit like a bank

that loans out gravity to nearby dwarf galaxies to make

them more stable. However, there are conditions on the

loan: if the dwarf galaxies start to approach the bank, the

loan is gradually reduced or even cancelled and the dwarfs

must pay it back. In two galaxies, we've seen what could

be signs that they've come too close too quickly and are

unable to repay the loan fast enough. This appears to have

caused disruption to their equilibrium."

Angus used MOND to calculate the ratio of mass to amount

of light emitted by the stars in the dwarf galaxies from the

observed random velocities of the stars collected independently.

He also calculated the orbital paths of the stars in the dwarf

galaxies. In all eight cases, the MOND calculations for the

orbits were within predictions. For six of the eight galaxies,

the calculations were also a good match to expected values

for mass-to-light ratios; however for two galaxies, Sextans

and Draco, the ratios were very high, which could well suggest

tidal effects. The value for Sextans could also be due to poor

quality measurements of the galaxy's luminosity, which Angus

said are improving all the time for these ultra dim objects.

"These tidal effects can be tested by updating the 13 year old

luminosity of Sextans and making accurate observations of the

orbits of Draco and Sextans around the Milky Way. We also

need to carry out some detailed simulations to understand the

exact mechanisms of the tidal heating," said Angus.

If Newton's gravity holds true, the dark matter needed in the

dwarf galaxies has constant density in the center which is

contrary to theoretical predictions, which suggest density

should rise to the center.

"Even without direct detection, the dark matter theory is

difficult to prove or refute and although we may not be able

to prove whether MOND is correct, by carrying out these

kind of tests we can see if it continues to hold up or if it is

definitely ruled out," said Angus.

Original News Source: Royal Astronomy Society's National

Astronomy Meeting