intergalactic medium

9

Missing Matter Found, But Doesn’t Dent Dark Matter

“But this doesn’t eliminate the need for dark matter; it doesn’t touch that undiscovered 27% of matter in the Universe, not in the slightest. It’s another piece of that 5% that we know is out there, that we’re struggling to put together. It’s just protons, neutrons, and electrons, existing in about six times the abundance within these filaments as compared to the cosmic average. The fact that this filamentary structure contains normal matter at all is further evidence for dark matter, since without it there’d be no gravitationally overdense regions to hold the extra normal matter in place. In this case, the WHIM traces the dark matter, further confirming what we know must be out there.”

It’s no secret that if we look at the matter we see in the Universe, the story doesn’t add up. On all scales, from individual galaxies to pairs, groups and clusters of galaxies, all the way up to the large-scale structure of the Universe, the matter we see is insufficient to explain the structures we get. There has to be more matter, both normal (atom-based) matter and dark (non-interacting) matter, to make our theory and predictions match. In a wonderful new pair of papers, two independent teams have detected the warm-hot intergalactic medium along the large-scale structure filaments in the Universe. With six times the normal matter density, this accounts for a significant fraction of the missing normal matter in the Universe! It’s estimated that 50-90% of the baryons in the Universe are part of the WHIM, and this could be the first step towards detecting them. But it doesn’t touch or change the dark matter at all; we still need it and still don’t have it.

What’s the full story on the discovery of the missing matter? Find out over at Starts With A Bang on Forbes!

10

New Space Telescope, 40 Times The Power Of Hubble, To Unlock Astronomy’s Future

“But these potential discoveries are what we know we’re going to be looking for. With every new major technological leap forward we’ve ever taken in astronomy and astrophysics, the greatest achievements of all have been the ones we could not have anticipated in advance. The great unknowns of the Universe, including what it looks like in the faintest regimes, how the most distant stars, galaxies, gas clouds, and the intergalactic medium behaved at early times, and what it looks like beyond anything we’ve ever seen will all be exposed for the first time. It’s possible that we’ll learn we were quite arrogant and wrongheaded in a great multitude of arenas, but we’ll need this new, high-quality data to show us the way.”

If you were an observational astronomer, what would your dream telescope look like? It would have to be huge, with an incredible amount of light-gathering power. The quality of the optics would have to be pristine, and higher-precision than anything ever created before. It would have to have multispectral capabilities, extending beyond both sides of the visible light spectrum. And it would have to be in space, with no interference from our atmosphere. If we could build a telescope like that, so many things would immediately become possible. We’d be able to directly image perhaps 100 exo-Earths around nearby stars, including spectra of their atmospheres. We’d take images of Jupiter of the same quality that JUNO can, but from Earth’s orbit. We’d be able to measure the star clusters inside and gas halos surrounding every galaxy in the Universe to just a few hundred light year-precision. And we’d be able to take high-resolution images of the faintest, most distant galaxies of all, in just a tiny fraction of the time it’s taken Hubble to do it.

There’s a 15.1-meter space telescope that’s in design right now: LUVOIR. If everything goes well, it could be NASA’s flagship mission of the 2030s. Want to learn more? Here’s what it’s all about!

4

Dark matter is necessary for the origin of life

“Without the additional gravitation of a massive dark matter halo surrounding a galaxy, the overwhelming amount of material ejected from a supernova would escape from galaxies and wind up floating freely in the intergalactic medium, never to become incorporated into future generations of star systems. In a Universe without dark matter, we’d still have stars and galaxies, but the only planets would be gas giant worlds, with no rocky ones, no liquid water, and insufficient ingredients for life as we know it.”

Dark matter is necessary to explain the motions of stars, galaxies and the formation of structure in the Universe, but most surprisingly is how its presence and abundance is essential to the existence of life in the Universe.

My latest for Forbes!

6

Why do the tiniest galaxies have the most dark matter?

“When you get a large burst of star formation, you create intense, ultraviolet radiation. When the most massive stars die, they create bursts of supernovae, which ionize matter and accelerate it to near-relativistic speeds. And when you funnel matter into a black hole, it can cause jets, which eject matter into the intergalactic medium. All of these factors are at play in all galaxies, and yet these matter-ejecting effects only touch the normal matter. Because dark matter is transparent to all electromagnetic phenomena, only the normal matter gets ejected whenever you have a star-formation, stellar-death or black-hole-infalling event. On the other hand, these effects simply pass through the dark matter, and so it remains in these low-mass galaxies.”

When we look out at the Universe on the largest scales, from large-scale structure to the fluctuations in the CMB to lensed clusters of galaxies and to giant spirals and ellipticals, we find the same thing everywhere we look: dark matter outmasses normal matter by a 5-to-1 ratio. It’s a finding that’s independent of direction, scale or distance. But when we go smaller, to tiny dwarf galaxies, we find that dark matter plays an even greater role, outmassing normal matter by factors of dozens, hundreds or even thousands-to-one. The tiniest galaxies somehow have the most dark matter, with the smallest galaxies of all containing only a few hundred low-mass stars yet nearly a million solar masses of dark matter. Yet this is no mystery; the physics of how normal matter gets ejected by star formation and other electromagnetic violence while dark matter is unaffected explains it all!

You’re Tearing it Apart

These four spiral galaxies in NGC 4410 display an extraordinary cosmic spectacle, each generating immense tidal forces that rip each other apart as they pass close to each other. The galactic disks and spiral arms stretch apart while stellar filaments swirl into the intergalactic medium as the galaxies entwine in a dance of staggering proportions.

Image Credit: Canada-France-Hawaii Telescope/Coelum

An astronomer has discovered a river of hydrogen flowing through space. The faint gas filament is streaming into the nearby galaxy NGC 6946 and may help explain how certain spiral galaxies keep up their steady pace of star formation.

“We knew that the fuel for star formation had to come from somewhere. So far, however, we’ve detected only about 10 percent of what would be necessary to explain what we observe in many galaxies,” said D.J. Pisano, a West Virginia University astronomer who used the 328-foot-diameter Green Bank radio telescope to make the discovery. “A leading theory is that rivers of hydrogen – known as cold flows – may be ferrying hydrogen through intergalactic space, clandestinely fueling star formation. But this tenuous hydrogen has been simply too diffuse to detect, until now.”

Read more about the image below.

Keep reading

3

A famous supermassive black hole ‘spied on’ with the Gran Telescopio CANARIAS

Cygnus A is an elliptical galaxy at around 600 million light years from the Earth, which has a supermassive black hole at its centre. It is one of the brightest sources of radio waves in the sky and featured in Contact, the famous science fiction novel by Carl Sagan which was made into a film. It has an active galactic nucleus which means that the black hole is “swallowing” material from its surroundings. When this occurs strong electromagnetic radiation is produced, as well as large jets of particles which are emitted from the galactic nucleus at a speed close to that of light, travelling beyond the edge of the galaxy and reaching three hundred thousand light years into the intergalactic medium.

This is the first time that polarimetric observations in the middle infrared region of the spectrum (1) have been made of the nucleus of an active galaxy. “The combination of the Gran Telescopio CANARIAS (GTC) and CanariCam offers unique capabilities for the observation of active galaxies using polarimetric techniques in the middle infrared” explains Enrique López Rodríguez, a researcher at the University of Texas in Austin (EE UU) and the first author of this study, published in the Astrophysical Journal. “There is no other comparable instrument of this kind, he stresses, and no such instruments are expected until the next decade, because the instruments which are being developed now cannot make polarimetric measurements”.

Polarimetry is the technique which studies the intensity and the orientation of electromagnetic waves. “If the observed radiation is polarized in a given sense and with a given dependence on wavelength we can obtain information about the physical mechanisms which produce the polarization. This technique helps us squeeze out the last drop of information from each photon picked up by the GTC” says López Rodríguez". “Polarimetry” he adds lets us eliminate from the observations all the light which is not affected by the magnetic field in the active nucleus, so that we can filter out everything which comes from other sources, such as the galaxy itself, or background stars. This gives us a much higher contrast when we observe the jets and the dust in the galaxy, while studying the influence of the magnetic field on both of them".

On the basis of these observations the astronomers have been able to detect that the plasma ejected from the active nucleus is spiraling around the magnetic field of the jet, which generates a type of radiation known as “synchrotron radiation”, produced by the rapid movement of electrons around magnetic fields. Although this phenomenon had been observed previously at other wavelengths, this is the first time it has been detected in the middle infrared, which has enabled us to confirm that the plasma in the jet of Cygnus A is highly confined by the effect of the magnetic field. These observations allow us to obtain information about the configuration of the magnetic field in the neighbourhood of the black hole (2), valuable information which cannot be directly observed.

A cosmic jigsaw
Astronomers classify Cygnus A as a radiogalaxy because it is one of the most powerful radio sources in the sky. It was observed for the first time in 1939 and it is named because it is the strongest radio source in the constellation of the Swan (latin name Cygnus). Nevertheless this galaxy emits radiation over the full range of the electromagnetic spectrum which makes it an ideal astronomical laboratory, and one of the favourite objects of astronomers, who have been making observations with diverse instruments and at different wavelengths, interpreting them to compose the pieces of a cosmic jigsaw which will let us understand better what is happening in that region of the universe.

Cygnus A has a very complex structure which includes a compact nucleus and opposed jets of matter emitted from the centre of the galaxy towards the edges, all shrouded in a mantle of dust with an irregular structure which is impenetrable to visible light. “It is a paradigm galaxy for studying the formation and evolution of jets, because the dust completely obscures the centre of the galaxy, so that we cannot detect well the light emitted by the jets” explains López Rodríguez.

This is why the research team has used CanariCam, and instrument designed to detect infrared radiation, which is not blocked by interstellar dust.

The Gran Telescopio CANARIAS is uniquely equipped to make these observations. Thanks to its large primary mirror, which favours high spatial resolution, and the CanariCam instrument, which can observe in the middle infrared wavelength range, we can study the infrared radiation emitted by the galaxy. This emission comes from matter which is not hot enough to emit visible light, but are warm enough (around 220K, which is -53ºC) to emit infrared radiation. In addition the polarimetric capability of CanariCam gives an additional dimension of information with which astronomers can analyze to interpret different physical mechanisms.

Until now very little has been known about the polarization of the infrared radiation emitted by the supermassive black holes which are at the centres of the majority of galaxies. Astronomers hope that these, and other similar observations can provide new data which will help them to understand the mechanisms which cause the activity of these cosmic monsters, and their influence on the galaxies which they inhabit.

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Notes:
[1] With the aim of explaining the dominant mechanism which polarizes the radiation from Cygnus A at infrared wavelengths this study presents polarimetric observations at high angular resolution (0.4 arcseconds) in the filters at 8.7mm and 11.6 mm, using the CanariCam instrument on the Gran Telescopio CANARIAS (GTC) of 10.4 metres diameter at the Roque de los Muchachos Observatory of the Instituto de Astrofísica de Canarias on the island of La Palma (Spain).
[2] For Cygnus A, the 65% of polarization measured in the middle infrared is close to the theoretical máximum of 70% which indicates that there is a highly ordered magnetic field around the nucleus of Cygnus A.

TOP IMAGE….This is a view of the jets of the elliptical galaxy in Cygnus A. Credit X-ray image: NASA/CXC/SAO; visible light image: NASA/STScI; radio waves image: NSF/NRAO/AUI/VLA.


CENTRE IMAGE….Novel observations by an international group of researchers with the CanariCam instrument on the Gran Telescopio CANARIAS provide new information about magnetic fields around the active nucleus of the galaxy Cygnus A. This is the first time that polarimetric observations in the middle infrared region of the spectrum have been made of the nucleus of an active galaxy. Credit NRAO.


LOWER IMAGE….This is a view of the jets of the elliptical galaxy in Cygnus A. Credit NRAO/AUI.