# Will stars on the other side of the galaxy affect gravity here?

• I
Gold Member
TL;DR Summary
Will the gravity of stars on the other side of Sagittarius not be blocked?
Does intervening mass between two stars decrease the gravitational attraction between these two stars?
Is gravity a local phenomenon in that local mass interacts with the surrounding gravitational field caused by the local star and distant stars?

Gold Member
2022 Award
What have you read about the extent of gravitational effect for a given object? What does General Relativity say that gravity IS ?

Mentor
I know I'm making it easy, but the simple answer here is "no", gravity doesn't get "blocked", it just decreases with distance. And yes, the galaxy's overall gravitational field is the sum of its parts.

Staff Emeritus
I know I'm making it easy

Nothing wrong with that.

Gold Member
If I say that a star on the other side of the galaxy has an almost negligible effect on our Sun. The main gravitational effect is due to Sagittarius. Is this statement correct?

Answering what General Relativity is: General relativity posits that gravity is a geometric property of four-dimensional spacetime. The curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by a system of partial differential equations. (Which I read about, but which are way above my level.)

Gold Member
2022 Award
If I say that a star on the other side of the galaxy has an almost negligible effect on our Sun. The main gravitational effect is due to Sagittarius. Is this statement correct?
Yes, but not because anything is "in the way" of its effect, just because it's so far away.

Answering what General Relativity is: General relativity posits that gravity is a geometric property of four-dimensional spacetime.
Exactly, which is why one thing doesn't have any effect on the gravitational impact of another thing, although their effects would be additive and a closer one will have a bigger effect (give similarities in mass).

Looked at another (simplistic) way, you can block EM radiation, but you can't block geometry and gravitational waves are geometry.

Klystron and russ_watters
Gold Member
If I say that a star on the other side of the galaxy has an almost negligible effect on our Sun. The main gravitational effect is due to Sagittarius. Is this statement correct?
It is correct, in that you say main effect - but notice that it is not exclusive of that distant star. That star still has an influence.

In the grand scheme of things - 'the other side of our galaxy' is pretty much next door, compared to say, the stars of the Andromeda galaxy. They too have an effect on our galaxy (and thereby on our Sun), even though they're 25 times farther away.

And then recall that even whole galaxy clusters affect each other with their gravity. It's all just stars affecting other stars.

256bits
Mentor
If I say that a star on the other side of the galaxy has an almost negligible effect on our Sun. The main gravitational effect is due to Sagittarius. Is this statement correct?
There are a hundred billion stars in the Milky Way, plus their satellites, black holes, dark matter, stray gases, etc. So sure, the fraction of that total mass carried by any one star is "negligible". It's possible to calculate exactly how negligible by picking a hypothetical star or a given mass and distance from Earth.

DaveC426913
Gold Member
IOW, negligible - times 100 billion (or even just 10 billion) - is no longer negligible.

Gold Member
It would be an interesting exercise for the OP to work out what the gravitational acceleration would be of some fraction of stars at some set distance from Sol.

For example:
1010 stars at a distance of 105 light years
has the same attraction as
104 stars at a distance of 102 light years.
or
1 star at a distance of 1 light year.

(That can't be right. That means 10% of the galaxy on the far side of the galaxy has more effect (4x more) on Sol than Alpha Centauri!)

Code:
Rationale:

Num.(Sol=1)    Dist (ly)
10^10           10^5
10^8            10^4
10^6            10^3
10^4            10^2
10^2            10^1
10^0            10^0

Last edited:
russ_watters
Staff Emeritus