Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst
arxiv.org
arxiv.org
Would love to be informed how wrong I got it!
> "Spectroscopic observations of the afterglow and the host galaxy provided a redshift of z = 0.151 (de Ugarte Postigo et al. 2022; Castro-Tirado et al. 2022; Izzo et al. 2022), corresponding to a distance of 749.3 Mpc."
3.262e6 (so about 3.3 million light years per megaparsec) * 749.3 gives 2.445 billion light years, so in the ballpark.
The key thing in getting these estimates is the complex business of standard candles, which are astronomical objects believed to have a well-defined luminosity so one can calibrate distances by looking at how faint they are. There are two major kinds used, Cepheid variables (which only cover the range from 1 kpc to 50 Mpc, so not useful here) and type 1a supernovae (which are rare):
> "Beyond the question of whether conditions in the early universe affect the luminosity of a type 1a supernova, a second problem besets this standard candle that severely limits its use: supernovae are rare in any given galaxy. They therefore cannot be used to determine the distance to any galaxy that we may be interested in. Their only uses are in calibrating other distance measures, such as the cosmological redshift, in testing cosmological theories, and in studying the surrounding of these supernovae. Current studies with these standard candles are examining the expansion of the universe at redshifts between z = 0.01 and 1."
https://astrophysicsspectator.org/topics/overview/DistanceEx...
It might be interesting to look at those cited papers to see exactly how they got that measurement but it's bedtime.
P.S. Crash Course Astronomy #25 (Distances) is a fun 10 min watch, great series overall:
Because of relativity and the expansion of space neither really has a meaning. It's like the idea of common time: when did something happen on Alpha Centauri? You can't really answer that. Light cones and spheres of influence and so on. "When" is only a valid question when the thing you're asking about isn't relatavistically far away. Deep stuff.
Source: I just read Carlo Rovelli's The order of time. Would be overjoyed if someone who knows what they're talking about would correct/enhance this response. :-)
I assume things get a little more interesting at big redshifts, because you really are moving at relativistic speeds wrt what you're observing. I don't know off hand how they handle that. I will say I'm pretty sure the reason cosmologists tend to talk in redshifts is that redshifts can be pretty much directly measured and actual distance is... tricky. If you haven't already looked into the "cosmic distance ladder" you're likely to find it interesting.
Source: we covered this stuff in a college class. My math is very rusty, but I did do the math.
But are we not moving in relation to Alpha Centauri at a fabulous speed, because all the galaxies are moving one way or the other and rotating as is Earth moving around the Sun and rotating around its axis?
In actual textbooks and technical papers, like this one, yes, that's correct; they don't talk about them because they're not directly observable, and deriving them from the things that are directly observable is model dependent. So they prefer to talk about the things that are directly observable, of which the key ones are redshift, apparent luminosity, and (for objects that are large enough, like galaxies) angular size.
The relativistic effects you mention are additional reasons why those things are not usually talked about in technical writings.
Pop science writings are another matter: many cosmologists do talk about how long ago and how far away in those contexts without taking the time to add the caveats about how we don't directly observe those things.
Seems like it's totally possible that something could be 4 billion light years away, or 8 billion light years away, and have the same red shift. Maybe sometimes gravitational lensing would help determine if a star is behind or in front of another? I wonder if it's pretty common to observe objects that are more blue shifted than something that is clearly closer to us.
In theory, of course this is possible. But in our actual universe, that's not what happens. In our actual universe, there is a close relationship between how far away something is and its redshift. Or, to phrase it in terms of direct observables, in theory we could have an object that was 4 billion light years away and an object that was 8 billion light years away, both with the same redshift--but they would be very different in terms of other observables like apparent luminosity and angular size. So in the general case, in theory, we would not expect any particular relationship between those variables.
But in our actual universe, there is a close relationship between all three of those variables: redshift, apparent luminosity, and angular size all vary in concert and are closely correlated. That kind of observation is what leads cosmologists to conclude that our universe is expanding.
> I wonder if it's pretty common to observe objects that are more blue shifted than something that is clearly closer to us.
It's not only not "pretty common", it never happens except for objects very close to us, cosmologically speaking--for example, the Andromeda galaxy is somewhat blueshifted, indicating that it is moving towards us, while the Magellanic Clouds, which are closer (they are satellite galaxies of our own galaxy), are not, AFAIK, blueshifted. But all of these objects are in the same local, gravitationally bound group as our galaxy, so their relative velocities don't tell us anything useful about the large scale behavior of the universe.
Is it more accurate to interpret inferred distances derived from redshift as an average estimate? If so it would be great if popular science reporting also included the confidence intervals
We don't estimate distances just based on redshift. We use all three of the observables I mentioned--redshift, apparent luminosity, and angular size--as inputs to estimate parameters in our cosmological models, and one of those parameters is the scale factor--the "size" of the universe, which is what is used in the model to ultimately get actual distances--as a function of time. The models of course have error bars--no model is ever exact--and some of those error bars are due to variations of the motions of individual galaxies from the idealized cosmological expansion in the models. So in that sense distances given by the models are a sort of estimate, yes, based on the average motion.
In the abstract, they reference the “z” variable of redshift in light (that has traveled for billions of years during which cosmic expansion continued and expanded the original distance) and kiloparsecs (referring to the much closer span of Milky Way through which the emissions traveled, from which they are drawing inferences about dust density therein).
Wild, cool stuff!
EG:
Planned Optical Srveys
The Hector Galaxy Survey
The Hector Galaxy Survey will use the Hector-I instrument on the AAT to collect resolved spectroscopy for 15,000 galaxies out to z < 0.1.
It will use the TAIPAN facility on the UK Schmidt Telescope at Siding Spring Observatory to collect spectroscopy for more than a million galaxies in the local Universe (z<0.3) that are brighter than i<17.
So, uhh, yeah, to a certain class of astro-geek z<0.3 is absolutely "local universe"
Unless that's changed in recent times.
Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Explorer, is a NASA three-telescope space observatory for studying gamma-ray bursts (GRBs) and monitoring the afterglow in X-ray, and UV/Visible light at the location of a burst.
It was launched on 20 November 2004, aboard a Delta II launch vehicle.
Headed by principal investigator Neil Gehrels until his death in February 2017, the mission was developed in a joint partnership between Goddard Space Flight Center (GSFC) and an international consortium from the United States, United Kingdom, and Italy.
The mission is operated by Pennsylvania State University as part of NASA's Medium Explorer program (MIDEX).
Recent Swift Operations Statistics
In the past 28 days, Swift has received 88 Target of Opportunity requests (3.1 per day), from 63 members of the community, for 82 different celestial objects.
In that time Swift observed 30.3 targets in 113.8 separate observations on average per day.
Swift was observing for 71.2% of the time, the rest of the time spent slewing or passing through the South Atlantic Anomaly.
Since launching in November 2004, Swift has performed 653,651 observations.
This sounds like scifi stuff to me lol:
> The South Atlantic Anomaly (SAA) is an area where Earth's inner Van Allen radiation belt comes closest to Earth's surface, dipping down to an altitude of 200 kilometres (120 mi). This leads to an increased flux of energetic particles in this region and exposes orbiting satellites (including the ISS) to higher-than-usual levels of ionizing radiation.
https://en.m.wikipedia.org/wiki/South_Atlantic_Anomaly
I'm a HUGE space nerd and never heard of this. What else do I have no idea about??
Or, more seriously, Magnetorquers for sat attitude control and stabilization are somewhat obscure given they rely on good knowledge of the earth's geomagnetic field which fluctuates daily.
https://en.wikipedia.org/wiki/Magnetorquer
Maybe Cryogenic Sapphire Oscillators (high precision clocks for gravity and other apps)?
https://www.uwa.edu.au/study/-/media/Faculties/Science/Docs/...
https://www.adelaide.edu.au/ipas/our-research/defence-securi...
Check out the Great Annihilator. Two black holes near our galactic core feeding off each other.
The world of GRB's and the interpretation of such highly energetic phenomena was decidedly speculative just a few decades ago, but increasingly gravitational waves, horizon telescopes etc pin down the fantastic world of general relativity with its spacetime singularities and other oddities as actually... real :-)
Just like quantum mechanics its quite hard to internalize these concepts. I suppose if we can somehow fix "politics" we'll have all the spacetime in the world to work things out.
Various astrophyicists are hardwired by early adoption to to use CGS electromagnetic units and don't feel obliged to follow no union rules . . . no one rejects their papers over units, so <shrug>.
A foe is a unit of energy equal to 1044 joules or 1051 ergs, used to express the large amount of energy released by a supernova.[1] An acronym for "[ten to the power of] fifty-one ergs",[2] the term was introduced by Gerald E. Brown of Stony Brook University in his work with Hans Bethe, because "it came up often enough in our work".[3]
(although my postdoctoral advisor claimed our weird units were intended to keep the physicists at bay.)