Massive radio survey reveals our universe’s structure at the largest scales – Space.com
Massive radio survey reveals our universe’s structure at the largest scales – Space.com
New observations suggest our estimates of the cosmic dipole effect are actually in line with the large scale structure of the universe.
(Image credit: MALS Team)
When we look out into the universe with our unaided eyes, we are really only seeing a small chunk of what’s actually there. That’s because there are parts of the electromagnetic spectrum that our visual faculties are not sensitive to.
Radiation is being emitted by all manner of cosmic phenomena across this spectrum, yet we’re only able to physically see wavelengths within the visible light range without the help of external tools — but luckily, astronomers have access to telescopes that allow them to observe the universe across this continuum.
The South African MeerKAT radio telescope is one such observatory, allowing astronomers to probe the radio band emissions of stars, blackholes and galaxies in the surrounding universe. Recently, an international team of astronomers from the MeerKAT Absorption Line Survey (MALS) used a vast catalog of radio sources captured by the MeerCAT radio telescope to make a measurement of a phenomenon called the “cosmic radio dipole.”
Observing the radio sky can give astronomers insights into the large-scale structure of the universe, as radio emissions from far off galaxies can travel through space on relatively uninterrupted trajectories. The MALS survey has produced an extremely sensitive catalog of close to a million radio sources in the sky because the team pointed the MeerKAT telescope array in 391 directions.
Related: How did the universe’s elements form?
“The depth and the expanse of this continuum catalog holds a unique position among modern radio continuum surveys,” Neeraj Gupta, an astronomer at the Inter-University Centre for Astronomy and Astrophysics (IUCAA) who leads the MALS project, said in a statement.
The cosmic radio dipole is an effect generated by the motion of the solar system through space as it orbits the center of the Milky Way galaxy, and as the Milky Way gravitationally interacts with other galaxies. The effect makes radio sources appear more numerous in the direction the solar system is traveling in, and less numerous in the opposite direction.
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The magnitude of this effect should be directly related to the velocity of the solar system through space — however, the effect has been found to be much higher based on previous measurements of the solar system’s motion through space.
This made astronomers question whether the dipole might not just be caused by the motion of the solar system through space, but rather by other radio sources (and therefore more galaxies) in the direction that the solar system is traveling. However, the new dipole measurement based on the MALS survey is aligned with predictions based on current measurements of the solar system’s movement through space.
Astronomers think this discrepancy may be related to the design of different surveys, where the MALS survey covered small patches of the sky to a very deep level. By contrast, other radio surveys have measured wider patches of sky but on much shallower scales.”Measuring the dipole is an extremely important test of cosmology, and can tell us whether our fundamental assumptions about the structure of the Universe are correct,” Jonah Wagenveld, an astronomer at MPIfR and lead author of the paper that reported the findings, said in the statement.
As the new findings reveal, radio astronomy offers scientists novel ways of observing the universe at the largest scales, and therefore, opportunities to test our best cosmological theories against observational data.
A pre-print about these results can be viewed on the paper repository arXiv and a paper has been published in the journal Astronomy & Astrophysics.
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Conor Feehly is a New Zealand-based science writer. He has earned a master’s in science communication from the University of Otago, Dunedin. His writing has appeared in Cosmos Magazine, Discover Magazine and ScienceAlert. His writing largely covers topics relating to neuroscience and psychology, although he also enjoys writing about a number of scientific subjects ranging from astrophysics to archaeology.
- I am not understanding why the number of “radio sources” should be higher in one direction and lower in the opposite direction due to Earth’s motion “through space”.
I would think that the number of sources should be the same in all directions, but the wavelengths of similar types of sources would be shifted by the same amount in opposite directions due to the relative speed differences.
Can somebody please explain why the number of sources changes? Is it just that the peak sensitivity of the detector is not broad enough to detect the shifted frequencies through the shifts?
- I find it curious that to my eye the resultant image of the movement looks so much like the yin-yang symbol. The ESA’s GAIA telescope team provided an image of the 3D relative velocities within the Milky Way. May well be just an artifact of the human ability to see patterns that make sense of random shapes, like seeing faces in the clouds. Still, I do find it interesting that across immense scales, the similar form, looking like the interaction of electrical dipoles, appears to repeat. I appreciate that mentioning electrical phenomena on cosmic scales gets shut down pretty quickly, but you now what they say about things that look like a duck and sound like a duck… Below are some of the GAIA composite images. The second one down is the 3D relative velocities I mentioned.
- The center anisotropy in the second image shows the rotation of the Milky Way galaxy. The outer, larger, anisotropy is from our galaxy’s motion through the universe, the velocity being relative to the CMBR.
- Our solar system has two, maybe more, accelerations on it. It has the rotational acceleration like the other members of the MW. But our MW also has an acceleration and a velocity. Like our system does.
Which is faster, the rotational velocity inside the MW or the whole MW velocity? And who knows, the MW might have a pitch.
The only thing we are allowed to measure is our local pitch. We have no way to determine the final velocity of our pitch. We’re not sure how far the pitches stack.
- The CMBR does seem to provide a reference for velocity that would seem to be consistent across the entire universe.
At least if the CMBR is really what we think it is and the universe is really as uniform as we theorize it to be.
- I have a hard time using the term uniform, with those huge galactic webs. Appears kinda stringy to me. But aren’t most of those structures, radio structures? Or are they confirmed with light? And x-ray?
Maybe they mean uniform webs.
- Classical Motion said:
I have a hard time using the term uniform, with those huge galactic webs. Appears kinda stringy to me. But aren’t most of those structures, radio structures? Or are they confirmed with light? And x-ray?
Maybe they mean uniform webs.
https://www.oxfordlearnersdictionaries.com/definition/english/uniform_2#:~:text=uniform-,adjective,parts%20and%20at%20all%20times
This is another good example of “the map is not the territory”.
“The word is not the reality”. Sometimes disguising “convenient” assumptions.not varying; the same in all parts and at all times
. . . . . . . . . unless, of course, we want to assume it to prove something else?
One might, perhaps, call this a convenient ‘fudge’?
Cat 🙂
The Big Bang theory is based on several assumptions, including:
The cosmological principle: The universe is homogeneous and isotropic on a large scale, meaning that it looks the same in every direction and has the same observational evidence available from any location.Oh yes. “On a large scale”. But let us not forget this assumption.
Then, all we know is completely the opposite.
Ergo, all we experience is insignificant, meaningless.
So we seem to have a paradox. Science is some local philosophy or we accept the assumption that the Universe is uniform and not as we perceive it.
So we are back to relativity (in general).
All we experience is probably irrelevant to the Universe at large.
But our science is based on what we observe. All else is philosophy.Are our scientific observations just local freaks, or is the Universe uniform?
And on what scale is uniform not uniform? And why?Does this make science subjective, which is not what it supposed to be.
Cat 🙂
- Trying to be more specific than philosophical:
The observation is that the universe does not appear to be uniform at any level when observed in radio frequencies – showing a strong difference in the number of detectable sources with direction.
But, the article states that this is somehow expected and consistent with a universe that is assumed to have uniform density at very large scales.
My question is how is this apparent inconsistency explained to show that it really is consistent.
The article states that the observation and theory are consistent, even though they appear to not be consistent. So, the article owes us an explanation.
Or maybe I should say it owes us some proof that a credible explanation actually exists. Unsupported assertions are viewed with skepticism, if not outright suspicion.
- Unclear Engineer said:
Trying to be more specific than philosophical:
The observation is that the universe does not appear to be uniform at any level when observed in radio frequencies – showing a strong difference in the number of detectable sources with direction.
But, the article states that this is somehow expected and consistent with a universe that is assumed to have uniform density at very large scales.
My question is how is this apparent inconsistency explained to show that it really is consistent.
The article states that the observation and theory are consistent, even though they appear to not be consistent. So, the article owes us an explanation.
Or maybe I should say it owes us some proof that a credible explanation actually exists. Unsupported assertions are viewed with skepticism, if not outright suspicion.
Then it seems that we are in agreement?
Cat 🙂
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Source: Space.com