Milky Way and Andromeda galaxies set to collide - update 2014

The Andromeda spiral galaxy. 

Image courtesy NASA.

A short time ago, in a galaxy very, very close by, a NASA satellite thought it detected a gamma ray burst in Andromeda.

It was a false alarm, but astronomers used the opportunity as a reminder that our galaxy and Andromeda are set for a head-on collision.

NASA's Swift satellite discovers and measures gamma-ray bursts, the most powerful explosions in the universe, and their afterglow in X-ray, optical, and ultraviolet wavelengths of light.

The space agency says the spacecraft is designed "with powerful telescopes and quick reflexes to capture gamma-ray bursts as they flash and leave a lingering afterglow."

On Wednesday, astronomers and astrophiles alike buzzed with the news that Swift's equipment had captured a powerful flash of gamma rays, believed to be coming from the Andromeda Galaxy.

Those who watch the sky were caught up in the possibility that a clashing pair of neutron stars or a bright X-ray source was acting up a mere 2.5 million light-years away, NBC News reported.

But, alas, the excitement was short-lived. By the time more raw data came in and the initial information was re-analyzed, the project team realized what they thought was a giant burst of radiation was not the dense remnants of dead stars crashing together.

"We... do not believe this source to be in outburst. Instead, it was a serendipitous constant source in the field of view of a BAT subthreshold trigger," Swift team member Kim Page wrote in a NASA message.

The reason scientists (and the Twittersphere) were in such a tizzy was because, "The Andromeda galaxy, known in astronomical parlance as M31, holds a special place in our own future," the New York Times wrote.

NASA astronomers announced in 2012 "with certainty" that the next major cosmic event to hit the Milky Way will quite literally hit the Milky Way.

Our galaxy will have a "titanic collision" with neighbouring Andromeda. Not only that, the Triangulum galaxy, M33, is likely to join in on the action, causing a three-galaxy pile-up (and could even merge with the other two), scientists said in a statement.

The Milky Way and Andromeda are the dominant members of a small family of galaxies called the Local Group. Family ties bind the bevy together in the form of their mutual gravity.

NASA sought to assure the world that the sun and Earth are unlikely to be hit by stars or planets from Andromeda because of the vast emptiness of the two galaxies.

So Earth, they said, should easily survive what will be a 1.9 million kilometer per hour (1.2 million mile per hour) galactic merger. Even at that speed, the event would take about 2 billion years.

"It's like a bad car crash in galaxy-land," Roeland van der Marel, an astronomer with the Space Telescope Science Institute in Baltimore, which operates Hubble, told the media.

Scientists said in 2012 the collision would take place in 4 billion years. But the New York Times reported Wednesday, “Recent measurements with the Hubble Space Telescope have confirmed that they will hit head on in about two billion years.”

Hubble Image: Asteroids collide at 11,000 miles per hour

Scientists have captured and studied the collision of two asteroids for only the second time in the history of astronomy. 

In the May 20 edition of the Astrophysical Journal Letters (currently online), UCLA's David Jewitt and colleagues report on observations from NASA's Hubble Space Telescope of a large asteroid that was hit by a much smaller one.

On Dec. 11, 2010, astronomers noticed that an asteroid known as (596) Scheila had unexpectedly brightened and was sporting short-lived dust plumes. Data from NASA's Swift satellite and Hubble Space Telescope showed that these changes likely occurred after Scheila was struck by a much smaller asteroid, probably in late November or early December. The shape, evolution and content of the plumes enabled the scientists to reconstruct what occurred.

The smaller asteroid crashed into Scheila with the energy of at least a 100 kiloton nuclear bomb. The smallest particles from the collision escaped, and the dust formed plumes. These plumes were barely visible when Hubble observed Scheila two weeks later, and within two months, the plumes were gone completely, along with the evidence that Scheila had suffered a violent collision.

"The Hubble data are most simply explained by the impact, at 11,000 miles per hour, of a previously unknown asteroid about 100 feet in diameter," said Jewitt, the Hubble team leader and a UCLA professor of Earth and space sciences and of physics and astronomy.

Asteroids are rocky fragments thought to be debris from the formation and evolution of the solar system approximately 4.6 billion years ago. Millions of them orbit the sun between Mars and Jupiter, in the main asteroid belt. At 70 miles in diameter, Scheila is one of the largest. It orbits every five years, at about three times the Earth's distance from the sun.

Three days after the outburst was announced, NASA's Swift Ultraviolet/Optical Telescope (UVOT) captured a spectrum of the asteroid to search for gas but found none. The absence of gas around Scheila led the Swift team to reject alternative scenarios where exposed ice accounted for the activity.

Hubble observations on Dec. 27, 2010, and Jan. 4, 2011, were best explained by a collision with a small asteroid impacting Scheila's surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Jewitt and his colleagues estimated the crash ejected more than 660,000 tons of dust - equivalent to nearly twice the mass of New York's Empire State Building.

"Previously thought to be beyond the reach of direct observation, collisions are the main process by which asteroids are destroyed and dust is made in the solar system," said Jewitt, who is a member of UCLA's Institute for Geophysics and Planetary Physics and lead author of the journal article.

"An asteroid collision with the Earth 65 million years ago wiped out the dinosaurs. So, although they're rare, it's important to use every example to figure out what happens when two rocks smash together at unimaginable speed."

The research is illustrated in a NASA-produced video.

Potentially hazardous asteroid identified - It will collide with the Earth in 2182

“The total impact probability of asteroid ‘(101955) 1999 RQ36′ can be estimated in 0.00092 — approximately one-in-a-thousand chance-, but what is most surprising is that over half of this chance (0.00054) corresponds to 2182,” explains to SINC María Eugenia Sansaturio, co-author of the study and researcher of Universidad de Valladolid (UVA).

The research also involved scientists from the University of Pisa (Italy), the Jet Propulsion Laboratory (USA) and INAF-IASF-Rome (Italy).

Scientists have estimated and monitored the potential impacts for this asteroid through 2200 by means of two mathematical models (Monte Carlo Method and line of variations sampling). Thus, the so called Virtual Impactors (VIs) have been searched.

VIs are sets of statistical uncertainty leading to collisions with the Earth on different dates of the XXII century. Two VIs appear in 2182 with more than half the chance of impact.

Asteroid ‘(101955) 1999 RQ36′ is part of the Potentially Hazardous Asteroids (PHA), which have the possibility of hitting the Earth due to the closeness of their orbits, and they may cause damages. This PHA was discovered in 1999 and has around 560 meters in diameter.

The Yarkovsky effect
In practice, its orbit is well determined thanks to 290 optical observations and 13 radar measurements, but there is a significant “orbital uncertainty” because, besides gravity, its path is influenced by the Yarkovsky effect.

Such disturbance slightly modifies the orbits of the Solar System’s small objects because, when rotating, they radiate from one side the radiation they take from the sun through the other side.

The research, which has been published in Icarus journal, predicts what could happen in the upcoming years considering this effect.

• Up to 2060, divergence of the impacting orbits is moderate;
  
• between 2060 and 2080 it increases 4 orders of magnitude because the asteroid will approach the Earth in those years;
  
• then, it increases again on a slight basis until another approach in 2162, it then decreases,
  
• 2182 is the most likely year for the collision.

“The consequence of this complex dynamic is not just the likelihood of a comparatively large impact, but also that a realistic deflection procedure (path deviation) could only be made before the impact in 2080, and more easily, before 2060,” stands out Sansaturio.

The scientist concludes: “If this object had been discovered after 2080, the deflection would require a technology that is not currently available.

Therefore, this example suggests that impact monitoring, which up to date does not cover more than 80 or 100 years, may need to encompass more than one century.

Thus, the efforts to deviate this type of objects could be conducted with moderate resources, from a technological and financial point of view.”