
Fastest star ever seen is moving at 8% the speed of light - DarkContinent
https://phys.org/news/2020-08-fastest-star.html
======
Karupan
It's funny how every time I read an astronomy headline mention the word
"visible", my brain immediately interprets it as a conventional photograph and
is slightly disappointed when there isn't one.

~~~
mulmen
Hah, thank you for summarizing this so well. I never really connected the dots
on “visible” = “can be observed”.

~~~
redis_mlc
Virtually no distant astronomical image is a normal photo that corresponds to
what the human eye would see.

They're multi-layer stacks of CCD observations filtered by frequency range,
with false colors then assigned, not three RGB layers. IIRC, typically there's
7 - 11 ranges, depending on the instrument.

So one of the layers included in the depiction might be infrared, then false-
colored into something the eye can handle.

Source: I worked in remote sensing.

~~~
sillysaurusx
Which file formats did you use?

One of my frustrations with ML is that almost no one seems to be training on
HDR data. It's all 8-bit RGB. There is a big opportunity here to train GANs on
raw sensor data.

But that raises the question of which file formats to focus on. Since you have
lots of image processing experience, I'm very interested in what the data
formats were like at your job. Was it proprietary formats? If so, were there
any advantages over e.g. the RAW file format? Is RAW sufficient for
standardizing "everything necessary to turn photon readings into a photograph
that appeals to the human eye"? E.g. if I gather thousands of RAW photos, do I
need any other information not present in the RAW file?

Mainly I am interested in any insights you gained on the job: you might know
of some unique advantage that certain data formats have over others. I'm
extremely interested in training ML models to synthesize _what comes into a
camera_ (photon readings), as opposed to _what the world looks like to the
human eye_ (RGB values).

(I apologize for not phrasing my questions more carefully. It's late. The
essence is that right now, most ML training operate in terms of RGB, yet there
seems to be many advantages to operating in "photon space". The trouble is,
it's effortless to gather millions of RGB photos -- but it seems very
difficult to gather a million RAW photos. I'm hoping someone knows of a
massive trove of "some kind of raw data that can be turned into RGB values" –
maybe that's RAW, maybe it's something else. Whatever it is, once I have it, I
can feed it through an ML model.)

~~~
formerly_proven
RAW from most cameras isn't "real RAW". Firstly it generally uses lossy
compression secondly a lot of cameras apply some minor corrections to "RAW"
data as well (e.g. noise reduction). Some would argue that most cameras can't
give you "real" RAW since most sensors perform noise reduction one way or the
other internally (e.g. most Sony sensors use correlated double sampling). Most
sensors use analog PGAs to amplify the pixel signals before A/D conversion
(that's the ISO setting)[2], which changes the characteristics of the sensor
quite drastically (not just dynamic range and noise, a lot of older sensors
had severe issues with tinting and banding at high gains). RAW formats are
generally linear (those used for moving pictures are sometimes log-encoded,
which makes more sense [1], but isn't "raw").

A library like libraw reads most RAW files and can give you an appropiately
(for the sensor used) debayered RGB image. These images aren't in a defined
color space; they're specific to every camera/sensor.

In the moving pictures space OpenEXR is a common format for "arbitrary"
images, since it allows any number of channels each with different formats
(e.g. you can have a file with 27 channels per pixel, some of which are float
and some of which are integer).

[1] E.g. 12 bit log encoding gives even resolution across more of the dynamic
range; a linear encoding gives half of each range to the brighter stop.

[2] Sensors that don't have PGAs simply have a fixed sensitivity. If the
camera offers an ISO setting, it is emulated in the digital domain by pulling
the image.

~~~
neilpa
I’m assuming PGA is Programmable Gain Amplifier? It wasn’t immediately obvious
from a web search.

~~~
formerly_proven
Yes. The basic structure of a CMOS sensor looks a lot like a DRAM array, but
instead of a capacitor you have a photo diode and the "bit lines" / column
lines go into a programmable gain amplifier and then into a 12 or 14 bit ADC
with some DSP [1] and a parallel-to-serial interface. The exposure is
determined by the readout (row for row), that's what gives you rolling
shutter.

Some sensors have global shutter instead, which makes it even more like DRAM:
Conceptually each pixel has a capacitor and a photodiode, and a transistor
connecting the two, all of these transistors are connected in parallel and
form the "global shutter signal".

Some sensors have faster ADCs and use one ADC for a bunch of columns, which
has been claimed as the source of column-banding in some sensors (unclear if
correct).

[1] Sensors that are intended for both photo and video typically support
things like _pixel binning_ , where the sensor itself averages e.g. 2x2 blocks
of pixels internally. A lower quality alternative is _line skipping_ , where
the sensor is told to only read out every nth line, thus reducing resolution
considerably. The higher quality alternative is " _full-sensor readout_ ",
i.e. the camera reads all pixels and downsamples the image to the video
resolution. I believe some (announced?) sensors can do this in the sensor
itself now.

Note: A lot of this is "somewhat informed speculation" on my part, because
image sensor manufacturers tend to be very secretive of their sensor's
details.

~~~
craftinator
Annnnd comments like this are why I'm on HN daily. Thanks for sharing your
knowledge!

------
rsecora
An observer near Sagittarius A* at the star S62 has just published a report
about us moving at 8% of the speed of light.

~~~
Luc
Us and every other star they observe. Curious that.

~~~
rsecora
Alpha Centauri Herald

Carbon based life at the third planet of our nearest G2V star still think they
are the reference of the universe. They continue to measure starts without
taking into account they are not alone.

And worst, they still jam the radio spectrum with nonsense TV commercials. We
Alpha-Centaurians have have the worst neighbors in the known universe.

~~~
ethbro
> _We Alpha-Centaurians have have the worst neighbors in the known universe._

Just wait until they see what we're like when we get there.

~~~
bargle0
They won’t let that happen, but they’re probably not worried that we’ll even
make an attempt.

------
pdonis
The actual preprint on arxiv.org is here:

[https://arxiv.org/abs/2002.02341](https://arxiv.org/abs/2002.02341)

------
P-NP
But what is the fastest known UNBOUND star that does NOT orbit a black hole?
As of November 2019, it was S5-HVS1. Its speed is over 1,700 km/s or 1,056
mi/s. That's about 0.57% of light speed. S5-HVS1 will be flicked out of the
Milky Way. The previous record-holder was US708, a white dwarf travelling at
1,200 km/s or 746 mi/s.

------
brainless
I find it really fascinating to think that when 60 minutes pass on star S62,
on Earth 100 minutes would have passed in the same duration. This is Sci-Fi
territory in my mind. I am having all sorts of difficulty imagining some
implications of this.

Does this roughly mean, things are "sped up" in S62 from our point of view, if
we could observe some activity on that star?

~~~
thdrdt
Last week I watched the movie Interstellar and I still don't get why the main
character could be younger than his daughter when he returns from space.

And I also don't get your comment. Probably because I don't get relativity.

If we send a clock into space it will just tick away seconds (a unit designed
by people). When it will return back to earth years later in my mind it just
ticked away the same amount of time as it would have on earth.

What am I missing about relativity?

~~~
qppo
Think about the starting positions on a track.

The track is divided into lanes and each player is set backwards based on
their lane by a fixed distance, despite the fact the finish line is in the
same position. This is because of the curvature of the track - if everyone
started at the same "line" across all lanes, the runners at the outer lanes
would be running a further distance than those on the inner lanes!

Gravity does the same thing to time itself. The curvature is not of a track
but of spacetime.

In Gravity, the main character starts at an inner lane and his daughter at an
outer one - but the starting line is the same across all lanes. Gravity bends
spacetime, such that the inner lane is shorter than the outer lane (in terms
of distance in time). So when they ultimately arrive at the finish line, the
daughter has traversed a longer path in the time dimension than her father.

~~~
chrisweekly
Awesome analogy!

------
monkeycantype
So if Copernicus and Einstein were drinking coffee with Galileo and Hawking on
a little planet orbiting this star, trying to formulate an Alpha
Sagittaricentric model of the galaxy, how much would Einstein and Hawking be
contributing to the conversation? How important is relativity to explaining
what they would be observing of the light from other stars?

~~~
BurningFrog
Relativity only matters at very high relative speeds, which hardly exist
inside the galaxy.

~~~
daveFNbuck
Is 8% of the speed of light not a very high relative speed?

~~~
mehrdadn
[Layman here] The Lorentz factor is 1/sqrt(1-v^2/c^2) = 1/sqrt(1-0.08^2) =
100.3%, so dilation effects would be obviously measurable but not particularly
huge (0.3%).

------
m0zg
Speaking of moving fast, is there anything in physics that limits how fast
things are moving in space? I don't mean the limit of speed (that is already
known) but realistically, how likely is there to exist, say, a tiny, fist-
sized asteroid moving at a slightly sub-luminal speed? Say, 0.9997C in our
frame of reference? And if such a thing were to exist, what would the
consequences of it colliding with the Earth be? For the reference, an US
quarter coin traveling at that speed has relativistic kinetic energy of 4.85MT
TNT. We obviously wouldn't be able to detect an object moving this fast, but
how likely is it to be out there?

~~~
whatshisface
There is always a reference frame where the rock isn't moving - and we all
agree something can stay still, so there's nothing in physics preventing it
from going as close to the speed of light as you want.

I don't know the details of what it would do if it was moving merely very
fast, but curiously if it was fast enough, I'm talking unbelievably
overwhelmingly fast, it would probably go right through without interacting.
Why? Well, if you whiz through the electromagnetic fields of all the atoms in
the earth fast enough, the forces won't have any time to transfer momentum one
way or the other.

~~~
formerly_proven
> Well, if you whiz through the electromagnetic fields of all the atoms in the
> earth fast enough, the forces won't have any time to transfer momentum one
> way or the other.

Yet sun sails work, despite being micrometers thick and interacting with
particles going very close to c (from the sail's PoV).

~~~
whatshisface
Solar sails interact with light. It's matter-matter interactions that drop off
in the high speed limit.

------
stevenpetryk
It's interesting to imagine that there's possibly other life in the galaxy who
are also interested in this star, and in SgrA* in general.

------
Balgair
If you were to look at this star in it's peak velocity relative to a
stationary observer, you would see a pretty big shift in it's color!

Say the star was our sun, with a peak frequency at ~525nm. For reference,
that's a good solid green, like that of fresh wet grass. If the star were
moving away from you at 0.08c, then the color would redshift down to 569nm, a
nice pale lime. If the star were moving toward you, then it would blueshift up
to 481nm, an ultramarine blue. You can see the colors by wavelength here:

[http://pages.cs.wisc.edu/~yetkin/code/wavelength_to_rgb/wave...](http://pages.cs.wisc.edu/~yetkin/code/wavelength_to_rgb/wavelength.html)

------
kazinator
> _In 2018, S2 made its closest approach to the black hole, giving us a chance
> to observe an effect of relativity known as gravitational redshift._

The reality seems more complicated because the star speeds up at the closest
approach. When it speeds up, it is subject to time dilation. Time slows down
more as it speeds up, and so any electromagnetic waves emitted by the body
will have a lower frequency.

The effect of the speed up is not separable from the fact that it has dunked
deeper into the gravitational field of the black hole, which also contributes
time dilation.

> _If you shine a beam of light into the sky, the light doesn 't slow down,
> but gravity does take away some of its energy._

The red shift that we see is purely a time dilation effect. So that is to say,
if there were, say, a 101.5 Mhz radio station on that star, we would see that
at a lower Mhz figure purely due to the oscillator of that station appearing
to be slower due to time dilation. Someone riding that star, clapping their
hands once per second might look like they are clapping once every 1.2
seconds.

The beam of light which is conveying to us the events from a source cannot
alter the frequency of those events, even if it changes speed along the way.
If we see 1000 events per second, then it means the source is generating 1000
events per second, according to our frame of reference. It cannot be that the
source is generating 1200, but then the light somehow subtracts from that due
to losing energy while escaping gravity.

------
kazinator
> _If you shine a beam of light into the sky, the light doesn 't slow down,
> but gravity does take away some of its energy. As a result, a beam of light
> becomes redshifted as it climbs out of a gravitational well._

This is not true; or at least not that simple.

Under general relativity, the speed of light is c only locally. A remote
observer can see a slowed down light.

It doesn't make sense that light could be _bent_ by gravity, but not slowed
down; and then there is the business of light not being able to escape from
black holes.

[https://physics.stackexchange.com/questions/59502/does-
gravi...](https://physics.stackexchange.com/questions/59502/does-gravity-slow-
the-speed-that-light-travels)

------
perl4ever
I'm curious - is this star likely to be "eaten" in the near future, and when
something like that happens, could it potentially create a dangerous gamma ray
burst or something?

I think I've read something about how the Milky Way's central black hole is
unusually quiet, and speculation whether that was a prerequisite for life to
develop.

~~~
pdonis
_> is this star likely to be "eaten" in the near future_

It wouldn't seem so. The distance of closest approach to the hole is still 215
times the hole's horizon radius. The star's orbit will, over a very long
period, decay due to emission of gravitational waves, so eventually it will
fall into the hole, but not any time soon.

~~~
perl4ever
Well, sure, if you consider just the two objects, but I would think the
neighborhood is dense enough that statistically something else might have a
close encounter and change the orbit.

------
pdonis
The article's title is somewhat misleading. The warping of spacetime that this
star is making visible is not the warping due to the star itself; it is the
warping due to the huge black hole at the center of our galaxy that the star
is orbiting.

------
rini17
There are surely red/yellow dwarf stars even closer to the black hole (beyond
our observational capability). The skies on their planets would be fascinating
(but hostile to life).

------
WarOnPrivacy
At the end of the universe, will the remaining stars will be the ones that
were traveling the fastest?

~~~
sushshshsh
Do you mean at the time end, or at the distance end?

These stars are orbiting black holes, so they aren't traveling linearly to the
distance end of the universe.

As for the time end of the universe, nobody knows for sure how the universe
will come to an end. But if these objects are very hot due to their speed,
then perhaps they will live a bit longer than others, unless they explode
before then :)

~~~
WarOnPrivacy
>Do you mean at the time end, or at the distance end?

Time. After entropy has had it's way, might there be some age-deferred stars
zooming around?

~~~
ColanR
I think they're just speeding towards the end of time faster than the rest of
us.

------
ssijak
8% speed of light relative to what?

~~~
TheGallopedHigh
Relative to the speed of Light. Because that is constant irrespective of the
frame of reference

~~~
zodiac
Your second sentence is true, but the first one doesn't make sense. A car
travels at about 0.000001% of the speed of light, yet when we measure car
speeds, they depend on the frame of reference.

------
mrfusion
I wonder if we could do a slingshot maneuver around this planet.

------
tus88
It probably emanates gravitational waves too.

------
amelius
Relative to what?

~~~
AnIdiotOnTheNet
Us, obviously. How else would we measure relative velocities?

------
Arnavion
Blogspam (but with worse editing) of [https://phys.org/news/2020-08-fastest-
star.html](https://phys.org/news/2020-08-fastest-star.html)

~~~
mmastrac
Thanks - this is much better.

> it visibly warps spacetime

The explanation for this part of the title was completely missing from the
original article. They _might_ have been talking about the red shift?

~~~
soulofmischief
> For years, S2 was thought to be the closest star to SgrA, but then S62 was
> discovered. As a team recently discovered, it's a star about twice as
> massive as the sun that orbits the black hole every 10 years. By their
> calculations, at the closest approach, its speed approaches 8% of the speed
> of light. _That 's so fast that time dilation comes into play. An hour at
> S62 would last about 100 Earth minutes._

~~~
Dylan16807
But time dilation at 8% of light speed is less than half a percent. The so-
called "blogspam" has that part much more right: "At eight percent lightspeed,
the time dilation effect for S62 just barely becomes noticeable"

So where did they get '100 minutes'?

I'm not sure what affect the black hole itself would have, maybe that makes a
difference?

~~~
soulofmischief
A back of the napkin calculation says 60m should be about 62.5m at that
velocity. I'm not sure where that came from either.

edit: 60.2, forgot to square the ratio.

~~~
Dylan16807
If you got a 2.5 minute difference, did you forget to square the .08? My
napkin says that 60 / sqrt(1 - .08^2) is 60.2

~~~
soulofmischief
I sure did forget, thanks for the catch.

------
sparrish
That's not a star... that's a starship! <grin>

------
johndoe42377
> spacetime

Abstract theoretical concepts do not exist outside sectarian consensus.

This phrase is equivalent of saying like 'numbers became longer' or similar
nonsense.

~~~
johndoe42377
Could any downvoters please provide information about any actual experiment
which proves existence of space-time being of different kind than existence of
a number.

Also it would be nice to see any non-interpreted physical processes which
involves space-time.

Thank you.

~~~
nuclearnice1
> any non-interpreted physical processes which involves space-time.

Two examples in this thread? Depending on the meaning of “non-interpreted”

> satellites cause time dilation that’s accounted for in GPS satellite clocks
> and the receiver clocks

And

> its speed approaches 8% of the speed of light. That's so fast that time
> dilation comes into play

~~~
johndoe42377
> meaning of “non-interpreted”

Literally. Not being interpreted to support or confirm a current theory.

The abstract system of two clocks and an observer is just nonsense, since the
first time it was introduced by Einstein. Abstractions put together to form
another abstraction with supposed properties.

Any two clocks, bring man-made devices to support an abstraction of the mind,
are _completely unrelated_ instead of measuring the same phenomena.

Time dilation is just an error of measurement and of confirmation bias.

I am still looking for an actual experiment and at least one real process.

~~~
ivalm
If you don’t like clocks then the nicest earth experiment are free electron
lasers. They basically rely on length contraction to create coherent light
waves (you accelerate electrons until magnetic undulators are spaced at target
wavelength due length contraction). You can dial whatever electron speed you
want and get corresponding wavelength (although no greater than the at-rest
spacing for obvious reasons) and it all perfectly matches relativistic
prediction and works well/incredibly reproducible.

[https://en.m.wikipedia.org/wiki/Free-
electron_laser](https://en.m.wikipedia.org/wiki/Free-electron_laser)

~~~
johndoe42377
Where is time in this setting? Synchronization of wave length does not involve
time. The device is made according the abstract, derived notion of time, same
as it used the notion of a number. Nature does not posses any numbers,
however. Mind of an intelligent observer does.

It is useless to argue on HN. I have literally 5 or 6 accounts banned for
attacking a textbook ideas. It is easy to trace them all using HN backend.

Most of current HN crowd assume that I am some flat earth anti 5G lunatic,
while I have background in philosophy, and down to earth physics way above
that of downvoters.

~~~
ben_w
> It is useless to argue on HN. I have literally 5 or 6 accounts banned for
> attacking a textbook ideas.

Then don’t.

> I have background in philosophy,

I have an A-Level in philosophy, but it’s a terrible grade and I don’t get to
make up for that in philosophical discussions by waving around my Software
Engineering degree.

> and down to earth physics way above that of downvoters.

That choice of phrase alone will make you look like a nut. Would you care to
rephrase that, with _specifics_? Do you work professionally with aerodynamic
simulations, for example? Or perhaps you want tell us about the video game
engine whose physics model you coded?

