What is a 'Rogue Star'?

A rogue star, also known as an intergalactic or orphan star, is a star that drifts through space without being gravitationally bound to a galaxy or star cluster. Unlike most stars, which exist within the structured environment of galaxies (like our Sun in the Milky Way), rogue stars are solitary travelers in the vast emptiness of space, moving independently without a nearby galaxy to call home.

Rogue stars can originate from several potential processes:

1. Galactic Interactions: In galaxy collisions or interactions, intense gravitational forces can pull stars out of galaxies and propel them into intergalactic space.

   
   

2. Stripping: During interactions with massive galactic clusters, gravitational forces (known as tidal forces) can strip stars from galaxies, leaving them to wander alone.

   
   

3. Early Universe Phenomena: Some rogue stars may have formed independently in the early universe, perhaps in small, loosely bound galaxies that later disintegrated or "bled" stars into space due to weaker gravitational pulls.

   
   

Rogue stars are intriguing to scientists because they offer a unique perspective on the history and structure of the universe, as well as a potential way to understand dark matter.

Here is a list of notable rogue stars and their past or future encounters with our solar system:

1. Gliese 710 (Constellation Serpens)

• Type: Rogue star, not a hypervelocity star.

  
  

• Speed: About 51,499 km/h.

  
  

• Visibility: Magnitude 9.66 (requires a telescope to observe).

  
  

• Approach Timeline: In approximately 1.29 million years, it will come within 4,303 AU of the Sun, closer than Pluto.

  
  

• Outcome: Will not collide with our solar system but will become the closest star to the Sun, surpassing Proxima Centauri's current distance of 4 light-years (268,142 AU).

  
  

2. V2689 Orionis (Gliese 208)

• Past Encounter: Passed Earth at a distance of 5 light-years around 50,000 years ago, farther out than Proxima Centauri.

  
  

• Current Status: This close encounter is over, and the star continues to travel away from us.

  
  

3. Scholz’s Star (Constellation Monoceros)

• Past Encounter: Estimated to have crossed through the Oort Cloud approximately 70,000 years ago.

  
  

• Effect on Solar System: No significant impact on Earth, but it may have nudged objects in the Oort Cloud.

  
  

4. HIP 85605

• Current Trajectory: Moving toward our solar system, expected to pass through the Oort Cloud.

  
  

• Approach Timeline: Estimated to arrive within 240,000 to 470,000 years.

  
  

• Potential Impact: May disturb the Oort Cloud, possibly redirecting comets toward the Sun. There will be time to address any threats posed by comet collisions.

  
  

5. Gamma Microscopii

• Past Close Encounter: Passed within 0.35 to 1.34 parsecs (1.1 to 4.3 light-years) of the Sun approximately 3.9 million years ago.

  
  

• Type: A large G-type giant star (G6 or G8III) with about 2.5 times the mass of the Sun.

  
  

• Impact on Solar System: Likely influenced the Oort Cloud, potentially sending comets toward Earth. Some impact craters on Earth may be linked to this encounter.

  
  

These stars demonstrate how close stellar encounters can potentially influence the solar system, particularly by disturbing the Oort Cloud and potentially sending comets inward. The timeframes for such encounters are vast, giving Earth plenty of time to prepare for any indirect effects.

Image:

Illustration of a 'runaway' white dwarf. Credit Robert Lea