The farthest star | Hacker News Reader

The farthest star

syfy.com

159 pointsyitchelle30 comments

Amazing to me is the causal influence this star has on the Earth from 9 billion light years away. Physically the influence is zero, but the meaning humans are able to give it, makes it huge.

It caused you to physically move your fingers and type that comment.

That's a cool observation. You could then forget about this whole event and remember it again at the age of 90 and write another comment saying "I remember back when this was discovered"

Human bodies are very chaotic in their responses to stimuli due to the ability to react to old old memories...

well my take away is that I now know that syfy has value beyond the occasional good sci-fi show. I never really perused their site and there seems to be a good number of interesting articles here.

the science behind this star's visibility is well beyond my understanding but the article did a good job of putting into terms I could make use of

Yeah! I was slightly off-put by the tone of the first paragraph or two of the article, but then it actually dug somewhat deeply, including technical charts from the report, and I went back and read the whole thing. A very nice article.

What is also amazing is that this star is very likely long dead, but we will only know in a few million years :)

This line from the article is wrong:

> Over nine billion light-years away.

With a redshift of z=1.49, the light from SN Refsdal was emitted 9.34 billion years ago, but the proper distance at the current time (a/k/a the co-moving distance) is 14.4 Gly due to the metric expansion of space:

https://en.wikipedia.org/wiki/SN_Refsdal

Here's the paper announcing the discovery:

https://arxiv.org/pdf/1706.10279.pdf

An amazing discovery. If we can see things that far away, it's a wonder what we'll discover when we keep improving telescopes, introducing new telescopes (e.g. Webb space telescope), and even build devices on other celestial bodies! I'm looking forward to a permanent telescope on the far side of the moon where Earthly signals are no distraction.

As for the article, it was distracting by the poor writing style (emphasis mine). It's frustrating to hear people say "like" and "literally" all the time in speech, but far worse to see it in written pieces:

- "...point source (literally, a dot of light)"

- "...galaxy, a star, you, me — bends space, literally warps it"

- "...too faint to see. Like, hundreds of times too faint"

It's a blog post rather than a proper article. And it's by Phil Plait (AKA "The Bad Astronomer") who has been writing with a similar tone for over a decade now.

I didn't notice the author, thanks for pointing out. I remember passing the time between college classes reading Bad Astonomy in the computer lab. In 1997. Over a decade for sure...

At least the author used _literally_ correctly? I mean, none of those look like they should have been _figuratively_ instead.

> [...] build devices on other celestial bodies [...]

You must probably want to put your devices in space.

" Holy yikes. Seriously, "...ctrl+w.

Holy Haleakala.

Here's a nice size comparison of objects in the universe.[1] According to that video (and a Wikipedia article on it[2]), the observable universe is 93 billion light years in diameter.

Yet the "farthest star" article says the farthest star is only 9 billion light years away, which is ten times closer than the diameter of the observable universe.

[1] - https://www.youtube.com/watch?v=4S69zZwYrx0

[2] - https://en.wikipedia.org/wiki/Observable_universe

Due to the finite speed of light and the expansion of the universe - with changing expansion rate - describing large scale distances in the universe is somewhat tricky. There are several different distances measures like proper distance and comoving distance. [1] I am totally not an expert on this but it is not necessarily contradictory that the observable universe is 93 billion light years across and that a star 9 billion light years away is halfway across the universe, those two statements may just use different ways of attaching a number to cosmological distances. The universe is only 13.8 billion years old and therefore no light could have reached us from more than 13.8 billion light-years away if the universe were not expanding.

[1] https://en.wikipedia.org/wiki/Distance_measures_(cosmology)

> Yet the "farthest star" article says the farthest star is only 9 billion light years away

I think you completely misread the article. This is the farthest star we've been able to observe directly at its normal luminescence, as in, not a supernova. Granted, it is due to gravitational lensing.

The article never says this is the farthest star that exists, simply the farthest (by far) that we've been able to directly observe.

What are the farthest stars we've been able to detect?

The farthest directly observed objects are galaxies and quasars, to about 13 billion light years from us. We have indirect evidence of individual stars that far out, but prior to this discovery the farthest directly observed star[1] (SDSS J1229+1122) was 55 million light years away, so this is quite a leap.

[1] http://www.skyandtelescope.com/astronomy-news/the-most-dista...

The news is that we can pick out a single star at that distance, due to a quirk of gravitational lensing. Normally we could only notice an entire galaxy.

There's also the metric expansion of space to consider:

https://en.wikipedia.org/wiki/Metric_expansion_of_space

"galaxies that are more than the Hubble radius, approximately 4.5 gigaparsecs or 14.7 billion light-years, away from us have a recession speed that is faster than the speed of light. Visibility of these objects depends on the exact expansion history of the universe. Light that is emitted today from galaxies beyond the cosmological event horizon, about 5 gigaparsecs or 16 billion light-years, will never reach us, although we can still see the light that these galaxies emitted in the past."

So we may be able to see light from objects that are further away today (if they still exist) but when they emitted the light they were closer than that.

You should read about the difference between comoving distance and proper distance.

I started to wonder how on earth it's possible we can see it if the amount of photons is still the same right? Well before I decided to blurt my unproductive comment here on HN I researched this article on Quora https://www.quora.com/If-photons-have-no-mass-then-how-does-... which says that gravity increases the photons energy, frequency and speed(I thought they travel at the constant speed of light?) as they travel through space allowing those faint objects to be still visible here on near-Earth space.

Yet if the amount of photons that travel is the same with a gravitional lense or not I'd argue that the information to see a lot of other distant and faint objects exists as well. We just need better instruments to detect them. And probably there is a threshold after which the photon's energy become so small that it regresses into a background noise. Well kinda obvious now that I wrote it down.

I think lensing implies we're receiving more photons that would otherwise be scattered elsewhere.

> Once they found it in the 2016 images, the astronomers found it in other data as well. The apparent brightness of the star changed over time in the images. While a blue supergiant can change its brightness, it’s more likely LS1 is moving as it orbits the center of its own galaxy, and as it does so the effects of the gravitational lens change.

Can gravitational lensing really affect the brightness of an star traveling around a galaxy within a few months timespan?

It doesn't affect the star, but it might influence the image of a star through the very imperfect lens formed by the foreground mass distribution.

"This is incredible: Due to a quirk of cosmic geometry, astronomers have detected the light from the farthest individual star ever seen."

That is perhaps the least incredible thing I have ever heard. In fact, it's very nearly a tautology.

The overall writing style of this article is very poor and distracting.

Your quote is incomplete, the next two sentences are an important part of it:

" How far away is it?

Over nine billion light-years away."

To see the light of a star that far away is indeed "incredible" as in "so extraordinary as to seem impossible".

The following paragraphs then explain why it appears to be legit (" Then I read the paper, played with the math a little, and, sure enough, this appears legit.").

> "The overall writing style of this article is very poor and distracting."

at least the article didn't resort to converting astronomical numbers into trips from NYC to LA...

It's Phil Plait; he's been writing like this for a long time. I generally like his stuff, but his "look how clever and in tune with the kids I am" overuse of "embiggen" makes me eye-roll every time.

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