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.
indeed, every time i see such articles i remember my high school teachers’ metaphor: in science when we “observe” a phenomena doesn’t necessarily mean that we see it literally, like when we drop a pen to the floor and we hear the sound, we know a pen has fallen to the floor although we haven’t actually seen it with our eyes
There is actually an inverse correlation between the directness of an observation and the quality of the data. The human brain and sensory system are remarkable, but also limited and easily fooled. It is optimized for detecting food and predators, and reading the facial expressions of other humans, not making scientific observations. This is why, when accuracy matters, we build machines to do the work of observing for us.
Thank you for pointing out the distinction between "direct" observation through human senses, and machine-mediated observation for accurate scientific measurements.
It clarifies the motivation for extension/augmentation of human perception through technology, from microscopes to telescopes - and spectacles/glasses for that matter.
It also implies a continuation of the trend, where more and more of human perception will be mediated by technology, to benefit from advantages like accuracy, long-term memory/storage for data collection and statistics.
I guess augmented/virtual reality is part of it, where we can now perceive and experience a fully technology-mediated world, both real and imaginary. I picture sci-fi possibilities, like being able to "zoom in" to see things at magnifications beyond human biological limits - all controlled by thoughts.
This is hacker news; have you never encountered the visibility of identifiers in a scope? Or the visibility of side effects of a body of code? Visibility of a host on a network? ...
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.
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.)
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.
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.
TIFF is kind of standard for most scientific imaging, from astronomy to biomedical.
12- or 16-bit greyscale is common, with multiple channels for hyperspectral data. But since it can also store 32-bit data, floats, and complex numbers as well as rationals, it can be used as a container for pretty much anything you want to throw at it.
Regarding RAW. It's often used with colour CCDs with various types of CFA, like Bayer or CMY. It might have a higher bit depth, but it's still basically RGB but spatially separated and stored as greyscale. You could maybe feed it directly to your ML, but it's more common to filter it to create RGB data retaining the bit depth but at the expense of low pass filtering to remove aliasing artefacts. Or keep the separation to keep the high frequency components; really depends upon what information you want to extract.
FITS is very domain-specific for astronomy. It's not at all common in the wider scientific community.
I used to work on on of the larger imaging tools, supporting over 150 scientific file formats. The vast majority, over 80%, were using TIFF as a container. The next most popular was HDF5. FITS was not something I saw commonly, and we were getting images from researchers all over the world.
If you want a terabyte or two of .CR2 (Canon’s “RAW” file format) files of astrophotography to train on, let me know. They were taken on a camera sensor that had a full spectrum IR conversion performed on it.
All I ask is that you share your findings with me and don’t redistribute the image data set without confirming with me.
Yes, absolutely! That sounds wonderful, and we certainly won't redistribute the data without asking.
We have a server with a 24TB NAS. If you send me your ~/.ssh/id_rsa.pub key, I can add you to it and you can upload straight to the NAS. Would that work?
I have an event to go to today, but if you hop into our ML discord server (https://github.com/shawwn/tpunicorn#ml-community) and DM me (I'm shawn), we can figure out the details. Or email me (shawnpresser@gmail.com).
Thanks so much! This is exactly what I had in mind when I was writing my comment. I think it would be straightforward to extend StyleGAN to synthesize full spectrum data. And the results would look pretty darn cool.
(Not astronomy) When I worked in particle physics it was all TIFF, and often forks of libtiff with non-standard extensions, with nothing under version control. In hindsight it was a miracle the images were readable from one month to the next.
What problem you try to solve with GANs? Your RAW HDR photos are really taken by a sensor with RGB mask filtering out whatever is not visible spectrum. Scientific or indistrial imaging mostly use monochromatic information which is later colorized for human eyes.
Even if you get millions of RAW photos they will come from different sensors with different properties (noise, sensitivity, mosaic, orientation...) and you need to to normalize them all. sRGB is most common normalization target for which all prosumer cameras are optimized for.
The format is not really important here as it is usually array of pixels. You need more bits and resolution? Fine, but you also get more useless noise.
Color and dynamic range of most sensors extends greatly beyond sRGB, it's the camera's JPEG processing engine which maps this larger range to the smaller sRGB (or AdobeRGB) range.
You can attach custom ICC profile to JPEG, also to TIFF or PNG. But still you need to normalize data from different kind of sensors before you feed any ML engine with it. sRGB or AdobeRGB are most common color space profiles you can get with varied content.
Well, in remote sensing it was mostly 8-bit data per frequency range, then each satellite or instrument by name (LANDSAT, GOES, SPOT, etc.) has its own file format.
Sometimes a CCD bit was stuck, so we would process around that, etc.
The terms "HDR" and "photo" are not commonly used.
The Perkin-Elmer military system has fortran source, so all the file formats are documented there (if you can get access), as well as a minimal Scottish university system.
That’s one and a half billion astronomical units. The star in question is twice the sun’s mass, and, I guess, not too dissimilar in size. If so, if you had a camera that could take a 1,000,000,000 by 1,000,000,000 pixel photo of our sun from the earth and pointed it at this star, that star would fill a single pixel (Likely a few more more due to imaging imperfections, but those would mean the light gets smeared out)
It typically takes multiple ‘photos’ to even get a single of those CD observations in a frequency range (https://en.wikipedia.org/wiki/S2_(star)#S0–102: “At one-sixteenth the brightness of S0–2, S0–102 was not initially recognized because it required many more years of observations to distinguish it from its local infrared background”
But if you were to use a teleporter to see these objects with your own eyes, they would match what is in the “photo”, right?
It’s not as though conventional cameras operate on the exact same principles as our eyes, either. And that’s without even getting into the amount of “computational photography” performed on phones.
Many objects are too dim to see with the naked eye even if you were close enough to see them. Even amongst those which are clearly visible, they’d appear quite a bit dimmer than they do in a long exposure photograph.
The Orion Nebula is a good target for grokking the difference. A long exposure photo with a DLSR (which will be blurry if you don’t have tracking) you’ll see lots of color. Through a pair of binoculars, you won’t although you will see the nebula.
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.
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.
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?
First, like others mentioned, they are way off in the effect size, for this kind of time dilation you need 80% the speed of light, not 8%.
Second, when looking at time dilation caused by velocity, it is always necessary to say who observes what since observers that move relative to each other won't agree on which clock runs at what speed. If the star moved at 80% of the speed of light, someone on that star would say "When a 100 minutes pass here, only 60 minutes pass on Earth" while an observer on Earth would say "When 100 minutes pass here, only 60 minutes pass on that star". So both observers would say that the other's clock is running slower than their own.
This answers a part of your last question - time dilation always makes clocks appear to tick slower than your clock if they move relative to you.
There are other effects that can make things appear "sped up", there's all kind of odd things happening when you go to high relativistic speeds ...
> Second, when looking at time dilation caused by velocity, it is always necessary to say who observes what since observers that move relative to each other won't agree on which clock runs at what speed.
Interestlingly, the universe does have a preferred velocity (and thus a preferred inertial frame). It's the speed and direction that makes the cosmic background radiation not have a dipole.
There is no center to the source of the background radiation, as it is was created at a moment the universe was still a fairly homogeneous soup (apparently) with these photons being created (and absorbed) everywhere roughly in equal quantity.
Only after the universe became transparent did these photons become free, and since they were produced roughly homogenously in that soup there are everywhere in the same quanitity: a background radiation.
Since they were not produced in a localized event, they won't have a center. But since they're everywhere, they are a sort of absolute reference for how fast you're going (actually that's a new and interesting idea for me too, pretty neat).
But if they're a reference for how fast you're going, aren't they also a reference for what direction you're going? Can you then not look backwards at the direction they have come from and work out the point that they all appear to originate from? And then haven't you found the centre?
Imagine an omnipresent and homogeneous field, let's say an infinite field of corn. By looking at the corn, you can see how fast you're going, without that observation requiring the field to have a center.
They are coming at you from every direction at once.
What you’re asking is analogous to asking where the center of the Earth is on a map of the surface, and arguing it must exist because of how things on the horizon change when you move.
The reference velocity is the one such that you see an equal amount of cosmic background radiation in every direction. If you're moving relative to it, you'll see extra radiation from in front of you (much like how you see extra cars moving in the opposite direction from you on a highway).
I never got a real answer to this thought experiment. It's something I always thought about but I've been too lazy and dumb to figure out. So say two people are hanging out in space and their watches are synced to 12:00, then one person blasts off, turns around then comes back.
`Clocks slow down when they move in relation to you`
So to the "stationary" person, the clock of the person who zoomed off would be behind. But since it's relative, to the "zoomer" the stationary person went out and back. So then to the zoomer the stationary person's watch would be slower.
But which one is it? Do they end up showing the same time?
It looks like someone (in addition to forgetting to clearly state where the observer is) forgot a zero when putting it in the calculator, at 80% of the speed of light you get the time dilation factor they state.
Furthermore they betray a Northist bias that I find disappointing in an Astronomy article, when they say, "In the Fall of 2022..." For half the terraqueous globe it will, in fact, be Spring. And anyway, I think they really meant "Autumn", dammit! </curmudgeonly>
Simpler Sci without the Fi, but still incredible to lay people, is that earth’s gravity and the movement of the satellites cause time dilation that’s accounted for in GPS satellite clocks and the receiver clocks. It’s amazing how much the Special Relativity and General Relativity influence our daily lives.
> It’s amazing how much the Special Relativity and General Relativity influence our daily lives.
I mean aside from the obvious one of it being an underlying theory for how the universe works and without it a lot of stuff would break it is really not that huge a part of most people’s lives. Sure, the GPS example is a fun one to bring up, but other than that there’s just a few things that we interact with that actually have a noticeable effect due to relativity, like some of the very characteristic properties of heavier metals or the design of particle accelerators, which many people used to have in their house until recently. And I guess you could go out and look at Einstein’s cross. But other than that it really doesn’t affect us that much.
You are absolutely right. I guess I was just fascinated because of the stated difference, which some have pointed out is off by a factor of 10! Yikes, so much for reporting.
You are re-experiencing the thought process of Einstein.
The recognition that there are consequences to our understanding of time if the speed of light is constant in every reference frame was earth shattering in the science community a century ago.
How would FTL communication work? Let’s assume we can literally communicate over any distance instantly. Do we come across as a bit slow to anyone orbiting star S62? “Wow, these earthlings sure are hard to work with. They just can’t seem to keep up!”
Do we have to remember that the people we communicate with have different experiences of time?
Gender identity, sexual orientation, native language. Temporal perception?
Honestly it doesn’t seem hard to overcome. But I do love the idea of shipping off a problem and having it done 20% faster.
But wait, aren’t they 20% farther along in evolutionary terms too? So isn’t that like a multimillion year advantage?
As others have commented, you can’t send information faster than light. This is because time itself doesn’t run off any kind of central clock. The relationship between two events in time changes depending on where the observer is. There is no way to perfectly synchronise two events which are separated in space. This is called the relativity of simultaneity. FTL communication results in paradoxes because of this.
There is an awesome article on wikipedia that describes it more. Totally blew my mind.
> Do we have to remember that the people we communicate with have different experiences of time?
This is already true on Earth. Different people process information at different speeds. Think about when you're talking to someone who is elderly. Do you slow down a bit so they have a chance to keep up?
Yep, exactly. I was just chatting with someone in the park today who was much slower to process and respond than I am accustomed to. I was able to adapt to that and we had a nice conversation. It’s definitely a thing. Communication is messy.
I do think this thought experiment is a bit different though. In the sense that everyone orbiting S62 is faster than us, by a considerable margin. There will still be individual variances of course but the baseline moves. It’s not just a way you adapt to an individual but to an entire group of people, based on properties of their location.
Reminds me of that star trek voyager episode with the fast moving planet “Blink of an eye” Hours in our universe, is centuries on this planet that orbits at an incredible velocity.
That episode was a (poor) adaptation of Robert L. Forward's first contact novel "Dargon's Egg". Humanity discovers life on a neutron star, where the intense gravity (billions of gs) enables degenerate matter chemistry where interactions are orders of magnitude faster than in conventional matter.
But the particular simplifying assumption you made invalidates the whole thought experiment. Who is moving faster actually depends on where you're looking from. This turns into complete nonsense if you assume instantaneous communication - who needs to slow down for whom?
> Let’s assume we can literally communicate over any distance instantly. Do we come across as a bit slow to anyone orbiting star S62?
Communicating "instantly" would be a paradox.
Remember there is no absolute reference to which speeds are measured, aka. a "luminiferous aether". Its existence was disproved in the 19th century.
So Earthers are slow for observers on that star, but inhabitants of that star are also slow for Earthers; because speed is relative. Hence the name relativity.
And the reason it doesn't result in a paradox with light-speed communication is that the increasing (resp. decreasing) latency between the two account for the increasing (resp. decreasing) difference of time caused by this discrepancy of an object speeding up away from (resp. toward) the other.
I think they’ll appear slower to us. We’d be sped up to them. I’d love to be able to travel at half the speed of light, a few months and I’d be able to return far in the future.
I’d hate to burst your bubble, but if you travelled at half the speed of light for what you think is a couple months, you’d come back in…a couple months. The dilation effect is only about 15% at that speed.
This is the plot of the book "planet of the apes". The explorers think they are on a different planet, until they realize they are in a future earth (because they travel at near the speed of light in their spaceship). (hope I don't spoil anything, it's such a classic).
I think its the opposite: things are slowed down on S62 so they can’t reach speed of light. That is how you could (in theory) go in the future because earth time would go faster if you were on S62. So if you could watch it, it would be slower?
Yet from S62's perspective, we're the ones moving.
It will be hard to imagine if you try to retain the concept of some universal clock. The important thing is that if you actually traveled from one to the other that during your accelerations time would warp around you so as to perfectly make both sides local clocks correct.
Sure, and knowing that they're the oddball doesn't mean their physics is any different locally.
This is the core concept of special relativity from which the rest is derived, neither of us is special in how our environment behaves. Whether you're on the spaceship traveling at 0.99c relative to earth or "at rest" (both are actually at rest but hopefully you know what I mean) everything feels the same as long as you are not accelerating.
But S62 is special because it's constantly accelerating very fast (going in orbit). And that makes it special and not equivalent to us. Twin paradox is very similar. It's an apparent paradox but not real.
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.
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.
Light travels at a fixed speed relative to the observer. If you shine it from a train it will move away from you at the speed of light. I am not standing on that train, it still moves away from me at the speed of light. This is where time dilation comes from.
The classic example is a clock of light ticking between two mirrors. If you are moving with that clock it is ticking at the speed of light. If I am in a frame of reference where the clock is moving perpendicular to the light tick's path, the light
will have a greater distance to cover. [1] Since the speed is fixed to me, this tick is slower.
It’s simple: You are familiar with how temperature works, right?
Imagine the same volumetric difference exists in 3d space, but the different regions are not hotter/colder, but time goes faster/slower.
So You get two identical clocks, showing the same time, and move one of them into a “slow time” region (which would be a star moving very fast (8% of lightspeed). Let some time pass, then re-join the two clocks.
Since they spent some time in regions with different “speed of time” they’ll show a different time.
It will have ticked away less seconds. Time runs slower the faster you move. From the perspective of each individual person they wouldn't be able to tell the difference, but when they come back together they'll have passed different amounts of time.
But doesn't Einstein not talk about how you observe the clock when you move away from the clock? So the clock keeps ticking the same time but you can't observe it because you are traveling at the speed of light.
So when you travel away from the earth at the speed of light you can't see the rotarion of the earth. But when you move back to the earth you are still just as old as the people who were the same age as you when you left?
I’m going to try a different thought experiment than the others.
Imagine your clock is an LED, a light sensor, and a mirror. The “tick” of this clock is: the LED sends out a brief flash of light, which travels to the mirror, bounces off, and returns to the sensor.
If this clock is stationary relative to you, the time of that tick is the distance between the three components divided by the speed of light (c = d / t).
If it is moving relative to you, the light has to be at an angle, shining at where the mirror will be by the time the light gets there. This is a longer distance, and so it ticks more slowly from your perspective.
Every atom in your body, or in a clock, is held together by forces that behave like the light in the example clock.
Give two people clocks and have them move relative to each other, and both think the other is slow. This leads to the “twins paradox”, and while I can say the answer involves acceleration, I don’t fully intuit it and can’t help you with it.
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?
[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%).
So none of the numerous blackholes in our galaxy have astrophysical jets? Seems unlikely, maybe small, thin, and/or far enough not to be observed, but that doesn't mean they aren't there.
Generally they're associated with quasars and formedby supermassive black holes at the centers of active galaxies, which our galaxy doesn't really qualify for. However, while relatively quiet, Sagittarius A* does accelerate things to fairly high speeds, and it is thought that it might have some faint jets and an accretion disk.
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?
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.
Yes, I understand that, that's why I'm asking not if such a thing is _possible_ but whether it is even remotely _likely to exist_, given what we know about the universe, how galaxies and stars came to exist, etc.
That is, in order for something to have this immense energy in our frame of reference, that something (or Earth) would have to get that energy somewhere. What I'm asking, essentially, is how likely is it that such conditions would exist at some point?
> 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).
One scenario that comes to mind is the frame of reference moving 0.49 c in one direction then the object in question moving 0.49 c in opposite direction.
Good point. So unless there's gas moving in the same direction at a similar speed, the object would, over a sufficiently long period of time, be slowed down by this gas.
The issue is that the ISM is incredibly thing. So it's one of those multiple incredibly large by incredibly small number cases and intuition doesn't work, you'd have to do the actual math. I.e. the timescales could be large enough that if some process could create such an object they could still cross between galaxies.
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:
> 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.
> 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.
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.
> 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.
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.
Probably not. The star passes closer to Sgr A* than any other at 16 AU - about the distance between the Sun and Uranus - but that still puts it a long way from the black hole's event horizon. Despite its huge mass, Sgr A*'s Schwarzchild radius is only 0.08 AU.
Still in the long-term, yes it probably will be eaten up. After all the galaxy's black hole must have fed on stars in order to reach the huge mass that it has now.
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.
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).
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 :)
Personally, this is one of my favorite Wikipedia articles. People talk about having a larger perspective, but this page outlines the extreme limits to that.
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.
> 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.
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?
At 8% of c time dilation & length contraction are about 0.3%. That’s definitely measurable, but whoever wrote this article clearly calculated values for 80% of c rather than 8%.
It's phys.org. Don't expect them to actually check the math. They're way off.
> I'm not sure what affect the black hole itself would have, maybe that makes a difference?
No, gravitational time dilation due to altitude above the hole is negligible for this case; even the distance of closest approach is still 215 times the horizon radius of the hole.
Is there a particular group associated with it these days? Back in the day it was hot rodders who were talking about fast cars. I wonder what the linguistic definition of a colloquialism's lifetime is, or if there even is one.
I say both wicked cool and booking it, FWIW. Mid-30s and not sure what group I might be associated with. I guess some people would call me a hipster maybe. Haven't owned a car yet.
> Back in the day it was hot rodders who were talking about fast cars.
I’m not sure where you’re from, but this is just simply not correct. I have never been in that group and I know lots of people who regularly use that phrase. It’s a fundamental colloquialism.
What are your standards for something being 'real'? Science is interested in validating theories. Theories which predict observations are considered validated (or at least not invalidated, to be really picky), and most people use that as a good indication of 'real' (and General Relativity has passed the tests of science multiple times with flying colors). It seems you have a different set of requirements, but you haven't stated them, other than numbers and spacetime don't meet them.
The whole point of general relativity is to explain the way that the universe behaves as modelled by spacetime (i.e. the Minkowski metric to start)
Does it really exist? Maybe, we don't know (Symmetries and space and time are one of the things we could have right today as opposed to the standard model which is fairly likely to not stand the test of time), but who are we to judge.
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.
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.
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.
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.
> 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?
> Time dilation as predicted by special relativity is often verified by means of particle lifetime experiments. According to special relativity, the rate of a clock C traveling between two synchronized laboratory clocks A and B, as seen by a laboratory observer, is slowed relative to the laboratory clock rates. Since any periodic process can be considered a clock, the lifetimes of unstable particles such as muons must also be affected, so that moving muons should have a longer lifetime than resting ones. A variety of experiments confirming this effect have been performed both in the atmosphere and in particle accelerators.
Though experiments are flawed in a way that a untyped logical statements may be - they mix and match abstract concepts with "concrete" ones so to speak. It is just a type error as multiplying birds by trees.
Everything which follow the famous two lighting and a train thought experiment is simply logially flawed. Full of type errors.
Time as we know it, which presumably could accelerate and what not does not objectively exist, exactly and precisely the way numbers does not exit outside one's mind. Relations are, numbers not. Processes are, time isn't.
You can refuse to call it 'time', but there's something that adjusts in an extremely predictable way that matches the relativity equations. And that something is what people are talking about. The measurements are very definitely correlated; they skew as predicted to high precision.
Do you have any objection to the output of the equations matching reality, or do you just object to how we interpret the equations? Because the former is physics, and the latter is philosophy.
If you have different physics, use it to make predictions, show those predictions are different from what the current physics says, and then do experiments to show your predictions are correct. Otherwise, you have nothing to say.
It also varies based on velocity. You can easily calculate the effect of gravity alone on a GPS satellite and it doesn't give you the right number.
But what's the difference between every physical process slowing down, versus time dilation? Unless you're arguing that somehow only clocks slow down, and not other things?
The LIGO experiment can measure the change in length of one arm compared to the other due to anisotropy in spacetime. I don't know how you could explain it without spacetime, so that sounds like non-interpreted.
Well if one tried to put a munition on target in real time (on the order of few seconds) with classical gravity calculations from 7.6km high (and while moving at a higher rate speed compared to said target), one might be surprised where it lands and less surprised when accounting for things like "time dilation".
