Hacker News new | comments | ask | show | jobs | submit login
Astronomers report the most distant radio galaxy ever discovered (phys.org)
31 points by dnetesn 6 months ago | hide | past | web | favorite | 13 comments

The crazy thing about this is that based on this article [1] and some simple calculations, this galaxy and us are moving away at 86 percent of the speed of light!

Every megaparsec of distance leads to an increase in relative speed of 70 km/s. A parsec is about 3.26 lightyears - so a megaparsec is 3.26 million light years.

Dividing 12 billion by 3.26 million gives us ~3680 megaparsecs of distance between us. Multiplied by 70 km/sec, we get a speed of 257,000 km / sec or 86% of the speed of light! (300,000 km /sec)

[1] http://curious.astro.cornell.edu/about-us/104-the-universe/c...

There are plenty of galaxies that we know of that are receding away from us faster than c.

More mindblowingly, there are galaxies that we can see light of that always have been receding away from us faster than c.

My understanding has always been that your first claim is not possible. Can you cite something to back it up and explain it?

The point is that the space between two objects is expanding. The expansion causes the distance to grow, and comes in addition to any relative motion between any pair of objects. So through local space each object moves slower than the speed of light, but the rate of change of the distance between them can be greater than c.

More details here: http://curious.astro.cornell.edu/physics/104-the-universe/co...


"Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe"


In the early stages of the Universe, Space-Time itself was expanding. Measuring speed of light stuff doesn't make much sense under those conditions.

I always thought that while speed of light was more or less constant, space was/is expanding everywhere at the same time. For distances big enough, that's faster than c.

So you can take that idea and compute a different result, does the speed of light imply a max separation (!!!). Assuming speed is linear with distance (just go with it so we can calculate it :-)), then that suggests a maximum size of the universe away from us!

It's not that much farther, 13.97 billion. (13.97 billion / 3.26 million * 70 = ~300km/sec).

But looking at the other posters comments, we could be moving away from someone at 2c, because if we were both moving at the speed of light in opposite directions the relative separation speed would be 2c, even though each is only moving at c in a different direction from an observer. Is that right? so maybe it's ~28 billion.

I know nothing about astronomy and don't see the significant of what you are saying, please elaborate. "Something at a huge distance from us is moving away quickly from us" does not tingle my pleb senses.

I am getting a sense that the author is implying that there was not enough time for that black hole to form in this "radio galaxy", which seems to imply our "age of the universe" theories might be off. I guess that's exciting on a macro, abstract level.

The author is speaking of the scale of the expansion of our Universe. Given the distance between us and that galaxy, the speed added by pure expansion of the space between us becomes a significant number.

How linearly does that scale as you approach the speed of light?

Speed of light affects how fast information (force) can be transmitted through spacetime. The expansion is spacetime itself growing - so it should be completely linear. This is the basis for the Alcubierre warp drive.

The speed of light is nothing special when we are talking about galaxies receding from each other due to expansion. You can go beyond c.

Applications are open for YC Summer 2019

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact