This is the Reason why the Disc of the Milky Way is so Thick

This is the Reason why the Disc of the Milky Way is so Thick

A massive collision, which took place at around 10 billion years ago, fed all the stars in the inner halo of the Milky Way.

Space might seem a pretty peaceful place from down here but a closer observation reveals that things are quite violent up there. Events like Supernovae, strikes from Meteors and Comets, and collisions on the Galactic scale clearly reflects the hostile environment of space. These collisions do not follow the traditional sense of the word and involve gravitational interactions. Colliding galaxies are very common during the phase of ‘Galaxy Evolution’. Our own galaxy, Milky Way, is not an exception in this regard as it might have hit a number of galaxies during its long journey. Recently, researchers have figured out that the ‘Thick Disc’ around the galaxy was formed as a result of one of such collisions.

According to the recent study, this massive collision is solely responsible for all the stars that we see in the dome-like structures that extend below and above the galactic plane (inner halo). In addition to that, it also increased the thickness of the galactic disc. Prior to this research, astronomers long believed that multiple small collisions led to all these stars in the halo but all of those collisions were at least 10 billion years old. However, things changed dramatically following this publication which was based on the most detailed and accurate map of the sky. The Gaia Satellite of the European Space Agency provided this critical information to the researchers, which allowed them to have a detailed look at the stars in the inner halo.

The stars in the inner halo of the Milky Way lack in the concentrations of heavier metals. This indicates that all these stars are very, very old because the metals were spread after the death of the first generation of stars that produced these metals. It guided astronomers that all these stars are incredibly old and the collisions that led to the generation of these stars are at least 10 billion years old. The analysis of the data, provided by Gaia, showed that most of these stars had a single source and they came from another galaxy named as ‘Enceladus’. Amina Helmi, an Astronomer at the University of Groningen, explained their work in the following words:

The motions of stars in the inner Milky Way’s halo as measured by Gaia reveal the presence of a single large “blob” or kinematic structure. When we examined the chemical composition of the stars in this structure, we found a very well defined chemical sequence which only happens if the stars were born in the same system (and beyond the Milky Way). There may be other objects also contributing stars to the halo, but none is as large as this one. It really dominates the inner halo.”

This study also offered an answer for a long-lasting mystery of our galaxy. The galactic disc of Milky Way can be divided into two unique fragments. The thinner of the two is 400 light-years thick and contains gas and dust in addition to stars. On the other hand, the thick disc (1000 light-years in thickness) is occupied only by the stars that are older than 10 billion years (similar to inner halo). The model proposed in the research suggests that a collision with a dwarf galaxy of the size of the Small Magellanic Cloud would have resulted in both these effects.

The researching team is pretty much confident about the existence of Enceladus because they found 13 globular clusters which could be associated with this dwarf galaxy on the basis of their orbits and composition of stars. A previous study of Gaia also found that the Milky Way collided with a satellite galaxy sometime between 8 and 11 billion years ago. Despite all that, there a lot of work to be done and scientists are hopeful that they will be able to dig out more information about the Enceladus event. Talking about that, Helmi said,

The next steps are to characterize the galaxy Enceladus better, and also the proto-milky Way now that we know how to separate the two. It will give us unique insights on how galaxies looked like in the early universe and at high redshift, insights that are not possible to obtain by imaging those galaxies with Hubble.”

Have a glimpse at the historic collision:

Computer Scientist by qualification who loves to read, write, eat, and travel

  •  
    16
    Shares
  • 13
  •  
  • 3
  •  
  •  
  •  
  •  
  •  

Leave a Reply

Your email address will not be published. Required fields are marked *