It’s possible that the Milky Way and Andromeda galaxies have already started exchanging stars, long before they are expected to merge. In 2012, NASA astronomers said that the merger will begin in about four billion years. In March 2022, research published in the Astrophysical Journal revealed that the collision between the two galaxies is already underway. The two spiral galaxies will form one giant elliptical galaxy in about five billion years

Stars are more common near the centers of each galaxy, but the average distance between stars is still 160 billion kilometers (100 billion miles). This is analogous to one ping-pong ball every 3.2 kilometers (2 miles). Thus, it is extremely unlikely that any two stars from the merging galaxies would collide. 

The Milky Way and Andromeda galaxies interact with each other gravitationally, causing the two galaxies to fall toward each other at a rate of about 37 miles per second (60 km per second). The halo of both the Milky Way and the Andromeda galaxy have started touching each other. The halo of a galaxy is essentially a large layer of gasses, space dust, and outlier stars that surrounds a galaxy. 

NASA’s Hubble shows that the Milky Way is destined for head-on collision with the Andromeda galaxy, but Earth and the solar system are in no danger of being destroyed. Eventually, our remote descendants could be living in a large elliptical galaxy.

The study concludes that it is highly likely that HVSs from Andromeda could indeed migrate to the Milky Way. Whilst they are not expected in their thousands, they are expected to distribute equally around the Milky Way centre

We tend to think of stars as stationery objects in the sky, except for their slow westward drift across the sky as the Earth rotates. The reality is different though, stars do move but due to the vast distances in interstellar space, that motion is largely not noticeable. There are exceptions such as Barnard’s star in the constellation Ophiuchus. This inconspicuous red dwarf star moves 10.39 seconds of arc each year (by comparison, the full Moon is 1,900 seconds or arc in diameter.)

Another type of star can be observed, hypervelocity stars (HVSs), and these are among the fastest objects in the Galaxy. They are defined as stars that have a velocity which is of the order 1,000 km per second and by comparison, the Earth travels through space at a velocity of around 30 km per second! The first was discovered in 2005 but since then a number of HVSs have been found, and some of them have the potential to escape from the Milky Way

Yes, it’s possible that the Milky Way and Andromeda galaxies have already started exchanging stars, long before they are expected to merge. When galaxies collide, new stars are born and gravitational forces are redefined, changing the entire galactic architecture. The Milky Way might contain thousands of stars that were expelled from Andromeda, our closest galactic neighbor, and may even have brought planets with them

The two galaxies are still 2.5 million light-years apart, but the merger has already begun. Although Andromeda is approaching us more than 2,000 times faster, it will take 4 billion years before the strike. The merger will totally alter the night sky over Earth but will likely leave the solar system unharmed. 

However, it is extremely unlikely that any two stars from the merging galaxies would collide. Stars are more common near the centers of each galaxy, but the average distance between stars is still 160 billion (1.6×1011) km (100 billion mi). That is analogous to one ping-pong ball every 3.2 km (2 mi).

It is just possible that the two galaxies have already started to exchange stars long before they are expected to merge. We tend to think of stars as stationery objects in the sky, except for their slow westward drift across the sky as the Earth rotates

Gravitational interactions between colliding galaxies could create new waves of star formation, supernovas, and even black holes

Yes, galaxies interact with each other. Galaxies are said to interact when their gravity begins to change their shape. Interactions can be minor, like a dwarf galaxy pulling on the spiral arms of a larger neighbor, or major, like two large galaxies colliding

Galaxies attract each other due to their gravitational force. More massive galaxies have a greater influence on other galaxies than less massive ones. 

Galaxies are moving away from each other on average, but there are gravitationally bound collections of galaxies called groups, clusters, and superclusters. However, scientists have discovered that the entire universe is expanding, causing all groupings of galaxies to move away from one another over time. 

When galaxies interact and merge, their interstellar gas can be compressed and driven to the inner regions through shocks and gravitational torques, triggering intense starbursts.

Galaxies are said to be interacting when they are close enough for the gravity to start changing their shape. These interactions can be small, or minor, like when a dwarf galaxy pulls on the spiral arms of a larger neighbour. They can also be large, or major, where 2 huge galaxies crash straight into each other

Here are some ways to tell if galaxies have interacted:

• Starbursts Some galaxies form stars at an exceptional rate, which is known as a starburst. Starbursts are associated with colliding galaxies and nearby merging galaxies. 
• X-ray binary stars and diffuse X-ray gas Telescope observations in different wavelengths can show how the interaction has unfolded over time. X-ray binary stars and diffuse X-ray gas indicate earlier waves of star formation. 
• Strong gravitational lensing Large galaxies and galaxy clusters can act like lenses. Their gravity distorts the structure of spacetime, magnifying light from more distant objects. 

Galaxy mergers in today’s universe are rare. Only about five percent of nearby galaxies are currently involved in interactions

Interacting galaxies typically swing by each other multiple times, each time compressing gas to form new stars. Telescope observations in different wavelengths show how the interaction has unfolded over time, with X-ray binary stars and diffuse X-ray gas indicating earlier waves of star formation

Here are some examples of galaxy interactions:

• Minor interactions A dwarf galaxy may pull on the spiral arms of a larger galaxy. A satellite galaxy may also disturb the primary galaxy’s spiral arms. 
• Major interactions Two large galaxies may crash into each other, leading to a galaxy merger. For example, the Milky Way and Andromeda galaxies are predicted to collide in about 4.5 billion years, resulting in a new galaxy. The Magellanic Stream is another example of a galaxy interaction, caused by the encounter between the Milky Way and the Magellanic Clouds. 
• Galaxy cannibalism A massive galaxy may disrupt and absorb the stars of smaller galaxies that orbit it. 
• Galaxy harassment The relative velocity between galaxies can cause them to experience weak encounters.

Galaxies are said to be interacting when they are close enough for the gravity to start changing their shape. These interactions can be small, or minor, like when a dwarf galaxy pulls on the spiral arms of a larger neighbour. They can also be large, or major, where 2 huge galaxies crash straight into each other

Yes, the Milky Way is an interacting galaxy. It’s the result of past mergers, and it currently interacts gravitationally with its satellites, exchanging stars in long streams. The Milky Way is also interacting with other galaxies, changing their motions and shapes. For example, the Milky Way and the Andromeda Galaxy, our nearest spiral neighbor, are headed toward each other. In about five billion years, they may collide and merge

As the two galaxies hurtle toward each other at 250,000 mph, their mutual gravitational pull begins to distort their shapes. The black holes in the center of the galaxies will merge, forming a new, larger galaxy. The stars in the galaxies are so far apart that the galaxies will pass through each other like ghosts

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