Galaxy with no dark matter? (NGC1052-DF2)

In summary: I don't know what. But it might do something.In summary, a recent article discusses the discovery of an ultra-diffuse galaxy, NGC1052-DF2, with a stellar mass of approximately 2×108 solar masses. The research found that the galaxy's velocity dispersion is less than 10.5 kilometres per second, indicating a total mass of less than 3.4×108 solar masses. This is much lower than expected and suggests that dark matter may not always be coupled with baryonic matter on galactic scales. The article is currently behind a paywall. Some possible processes that could separate normal matter from dark matter include cluster collisions or gas collapse during galaxy formation. However, the
  • #106
Grinkle said:
I propose that a reasonable definition of bends is something that does not follow a geodesic.

This is a reasonable definition of a path bending, yes; i.e., it's what it means to say that a circle, for example, is curved in Euclidean geometry, as opposed to a straight line. However, note that this definition of curvature is extrinsic--it depends on the curve being embedded in a higher dimensional space in a particular way.

However, when we say in GR that spacetime is curved, we are talking about intrinsic curvature--curvature that can be defined simply by the intrinsic features of the manifold, without making use of any embedding in any higher dimensional space. There is no such thing for a one-dimensional curve; the lowest dimension a manifold can have and have intrinsic curvature at all is 2. And in 2 or more dimensions, the definition of "curved" is "has a nonzero Riemann tensor"--or, to put it in more concrete terms, that parallel transporting a vector around a closed curve does not leave the vector unchanged.

Grinkle said:
Its shape, whatever it is, defines straight. Any two points in a spacetime are connected by a geodesic.

This is true, but it only means that we can always find a straight curve--straight in the sense of extrinsic curvature, i.e., no bending of the path, i.e., a geodesic--between any two points. It does not mean that there is no difference at all between, for example, a flat Euclidean plane and a 2-sphere like the surface of the Earth. There is; but that difference cannot be captured by just looking at individual geodesics. You have to look at how multiple geodesics "fit together", so to speak--for example, by looking at what happens to a vector when you parallel transport it around a closed curve composed of geodesic segments, which is what the Riemann tensor describes.
 
Space news on Phys.org
  • #107
@PeterDonis Can you recommend a lay-person book or textbook on whatever math it is that is behind what you are describing?

I have in my (distant) past 4 semesters of calculus and 2 semesters (one undergrad and one grad) of engineering analysis, stated to give an idea of whether I am in any position to study this math.
 
  • #108
Grinkle said:
Can you recommend a lay-person book or textbook on whatever math it is that is behind what you are describing?

Carroll's online lecture notes on GR give a good introduction to the math of manifolds, tensors, and curvature in the first couple of chapters:

https://arxiv.org/abs/gr-qc/9712019
 
  • Like
Likes Grinkle
  • #109
kimbyd said:
To clarify, based upon our understanding of quantum mechanics, everything in the universe is made out of fields, and fields can be quantized into particles.
I would not put it like this as it seems to put an equal sign between quantum fields and particles. Particles are a particular type of state of a quantum field, but the phenomenology would be so much more dull if they were the only type of state. Only considering particles you miss out on any non-perturbative effects as well as the coherent states (and thereby the classical limit).
 
<h2>1. What is a galaxy with no dark matter? </h2><p>A galaxy with no dark matter is a unique and rare type of galaxy that has been recently discovered. It is characterized by a lack of dark matter, which is a mysterious substance that makes up about 85% of the total mass of the universe. This type of galaxy challenges our current understanding of how galaxies form and evolve.</p><h2>2. How was NGC1052-DF2 discovered? </h2><p>NGC1052-DF2 was discovered in 2018 by a team of astronomers using the Dragonfly Telescope Array in New Mexico. They were conducting a survey of ultra-diffuse galaxies, which are galaxies with very low surface brightness, and came across this galaxy with no dark matter.</p><h2>3. How do scientists know that NGC1052-DF2 has no dark matter? </h2><p>Scientists determined that NGC1052-DF2 has no dark matter by measuring the velocities of stars within the galaxy. In a galaxy with dark matter, the stars should be moving at certain speeds based on the amount of dark matter present. However, the stars in NGC1052-DF2 were found to be moving much slower than expected, indicating that there is no dark matter present.</p><h2>4. What does the discovery of NGC1052-DF2 tell us about dark matter? </h2><p>The discovery of NGC1052-DF2 challenges our current understanding of dark matter and its role in galaxy formation. It suggests that dark matter may not be as essential to the formation and evolution of galaxies as previously thought. This discovery also opens up new possibilities for studying the properties and effects of dark matter.</p><h2>5. Are there other galaxies with no dark matter? </h2><p>As of now, NGC1052-DF2 is the only galaxy that has been confirmed to have no dark matter. However, there have been other galaxies that have been observed to have very little dark matter, such as NGC1052-DF4. Further studies and observations are needed to determine how common these types of galaxies are and what implications they have for our understanding of dark matter.</p>

1. What is a galaxy with no dark matter?

A galaxy with no dark matter is a unique and rare type of galaxy that has been recently discovered. It is characterized by a lack of dark matter, which is a mysterious substance that makes up about 85% of the total mass of the universe. This type of galaxy challenges our current understanding of how galaxies form and evolve.

2. How was NGC1052-DF2 discovered?

NGC1052-DF2 was discovered in 2018 by a team of astronomers using the Dragonfly Telescope Array in New Mexico. They were conducting a survey of ultra-diffuse galaxies, which are galaxies with very low surface brightness, and came across this galaxy with no dark matter.

3. How do scientists know that NGC1052-DF2 has no dark matter?

Scientists determined that NGC1052-DF2 has no dark matter by measuring the velocities of stars within the galaxy. In a galaxy with dark matter, the stars should be moving at certain speeds based on the amount of dark matter present. However, the stars in NGC1052-DF2 were found to be moving much slower than expected, indicating that there is no dark matter present.

4. What does the discovery of NGC1052-DF2 tell us about dark matter?

The discovery of NGC1052-DF2 challenges our current understanding of dark matter and its role in galaxy formation. It suggests that dark matter may not be as essential to the formation and evolution of galaxies as previously thought. This discovery also opens up new possibilities for studying the properties and effects of dark matter.

5. Are there other galaxies with no dark matter?

As of now, NGC1052-DF2 is the only galaxy that has been confirmed to have no dark matter. However, there have been other galaxies that have been observed to have very little dark matter, such as NGC1052-DF4. Further studies and observations are needed to determine how common these types of galaxies are and what implications they have for our understanding of dark matter.

Similar threads

  • Astronomy and Astrophysics
Replies
11
Views
668
Replies
2
Views
693
Replies
4
Views
877
Replies
23
Views
1K
Replies
12
Views
2K
Replies
3
Views
1K
Replies
1
Views
1K
  • Cosmology
Replies
1
Views
909
Replies
1
Views
1K
Replies
5
Views
906
Back
Top