Seeking Missing Matter in Hot Halos

Could "missing" matter be found in the extended halos of spiral galaxies? Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA);  Acknowledgment: W. Blair (STScI/Johns Hopkins University) and R. O’Connell (University of Virginia)

Many galaxies seem to have far less visible matter than expected. In a new article, astronomers have taken the search for missing matter to the outskirts of spiral galaxies.

Messier 51, the Whirlpool Galaxy, is one of the many recognizable galaxies investigated in this work. The galactic halos studied in this article likely extend hundreds of thousands of light-years into space — far larger than the galaxies’ starry disks. Messier 51’s disk is 76,000 light-years in diameter. Credit:NASA, ESA, S. Beckwith (STScI) and the Hubble Heritage Team (STScI/AURA)

Misterious Matter

Just 15% of all the matter in the universe is thought to be visible matter — the kind we interact with on a daily basis — with dark matter making up the remaining 85%. Though dark matter is certainly the more elusive of the two, visible matter isn’t without its mysteries — after adding up the masses of the visible components of galaxies like stars and gas clouds, most galaxies appear to have less visible matter than expected based on observations of galaxies early in the universe. Milky Way-like galaxies seem to lack about 70% of their mass while low-mass galaxies can be missing all but a few percent.

Where might this missing matter be hiding? One possibility is that much of the mass of galaxies lies in extended halos that stretch hundreds of thousands of light-years beyond the bright, starry regions that make up the main body of a galaxy. This gas is difficult to detect because of its low density and interference from intervening gas within our own galaxy. How, then, can we weigh this halo gas?

A map of temperature fluctuations in the cosmic microwave background from WMAP. This map shows temperature deviations of up to 200 microkelvin. Credit: NASA

A Sunyaev–Zeldovich Stack

A team led by Joel Bregman (University of Michigan) searched for missing matter in galactic halos by looking for evidence of the Sunyaev–Zeldovich effect — the process through which low-energy photons from the cosmic microwave background are kicked up to higher energies through interactions with extremely hot gas. The magnitude of this effect is proportional to the mass and temperature of the gas, making it a useful probe of hot, diffuse halos that might otherwise be impossible to spot.

Bregman and collaborators used this method to investigate the halos around 12 spiral galaxies located 10–33 million light-years away — close enough to determine the spatial extent of the hot halo gas. Most of the halos were too faint to be detected individually, so the team stacked the observations from 11 of the 12 galaxies (one galaxy showed significant differences and was analyzed separately) to extract a signal and determine the average properties of the galaxies in the sample.

The integrated Sunyaev–Zeldovich signal from the stack of 11 galaxies as a function of radius (left) and the signal to noise ratio (right).  Credit: Bregman et al. 2022

Luminous Matter at Large

Bregman and coauthors found that out to a radius of 815,000 light-years (250 kiloparsecs), each galaxy contains 98 billion solar masses of gas. Each galaxy is expected to contain about 310 billion solar masses of visible matter, so this constitutes about 30% of the galaxies’ total mass. The galaxies’ stars, star-forming gas, and cooler halo gas make up a further 30%, meaning that the remaining 40% of the visible matter in these galaxies likely resides at even larger distances.

In order to search for gas even farther out, the team hopes to stack observations from more galaxies and develop new algorithms to reduce uncertainties. Proposed cosmic microwave background detectors like the Probe of Inflation and Cosmic Origins may also aid the search for missing matter, helping us understand where present-day galaxies hide their mass.

Citation

“Hot Extended Galaxy Halos around Local L* Galaxies from Sunyaev–Zeldovich Measurements,” Joel N. Bregman et al 2022 ApJ 928 14. doi:10.3847/1538-4357/ac51de

 

By Kerry Hensley

Source:American Astronomical Society - ASS Nova

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Magnetic Chaos Hidden Within the Whirlpool Galaxy

Magnetic field streamlines detected by SOFIA are shown over an image of the Whirlpool galaxy, M51, from NASA’s Hubble Space Telescope. For the first time, SOFIA’s infrared view shows that the magnetic fields in the outer arms do not follow the galaxy's spiral shape and are instead distorted. The intense star formation activity in these regions, shown in red, may be causing the chaos, along with the forces from the yellow neighboring galaxy, NGC 5195, tugging on one of the spiral arms. Credits: NASA, the SOFIA science team, A. Borlaff; NASA, ESA, S. Beckwith (STScI) and the Hubble Heritage Team (STScI/AURA). Hi-res image

Not all appears as it would seem in the Whirlpool galaxy. One of the best-studied spiral galaxies and a delight to amateur astronomers, Messier 51, as it’s officially named, is influenced by powerful, invisible forces.  

Located 31 million light-years away in the constellation Canes Venatici, the galaxy’s arms are strikingly visible as they reach out along the central spine structure, displaying swirling clouds of gas and dust that are massive star-making factories. But new observations by NASA’s Stratospheric Observatory for Infrared Astronomy, or SOFIA, presented at this week’s 237th meeting of the American Astronomical Society, shows  a more complicated picture.  

Radio telescopes previously detected neatly-drawn magnetic fields throughout the length of the galaxy’s massive arms. But under SOFIA’s infrared gaze for the first time those lines give way to a chaotic scene in the outer spiral arms. Using a far-infrared camera and imaging polarimeter instrument called the High-Resolution Airborne Wideband Camera, or HAWC+, researchers found that the magnetic fields in the outskirts of the galaxy no longer follow the spiral structure and are instead distorted. 

What’s causing all this magnetic pandemonium? The intense star formation in these areas creates chaos that can only be seen with infrared flight. A nearby, yellowish galaxy called NGC 5195 tugging at the outermost tip of one of the arms adds to the turmoil, possibly strengthening the magnetic fields. The research builds on SOFIA’s previous findings that show magnetic fields are important in shaping spiral galaxies and helps unravel the complex role magnetic fields play in the evolution of galaxies. 

Media Contact: 

Elizabeth Landau 
NASA Headquarters, Washington 
202-358-0845 
elizabeth.r.landau@nasa.gov 

Alison Hawkes 
NASA Ames Research Center, Silicon Valley, Calif. 
650-604-4789 
alison.hawkes@nasa.gov 

Editor: Kassandra Bell

 

Source: NASA/Galaxies

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Imaging an Expanding Supernova Shell

An optical image of the galaxy Messier 51 with the insert showing the location of supernova SN2011dh. Using precise radio imaging techniques, astronomers have determined the size of the shock around this supernovae, and estimated its outward velocity. Credit: Rafael Ferrando, Observatory Pla D’arguines

Supernovae, the explosive deaths of massive stars, are among the most momentous events in the cosmos because they disburse into space all of the chemical elements that were produced inside their progenitor stars, including the elements essential for making planets and life. Their bright emission also enables them to be used as probes of the very distant universe. Not least, supernovae are astrophysical laboratories for the study of very high-velocity shocks and the physics of particles under extreme conditions.

On May 31, 2011, an amateur astronomer spotted a supernova in the relatively nearby Whirlpool Galaxy (Messier 51), about 257 million light-years away. An analysis of the spectrum of SN2011dh showed that the precursor object was a massive supergiant star, about thirteen times bigger than the Sun (there is also some evidence for the presence of a binary companion star). The explosion set off a shock wave whose bright optical emission comes primarily from the inner dense, slow-moving ejecta. In addition, astronomers see a fast-moving component to the shock that is bright at radio wavelengths. The size and expansion velocity of the shock are thought to be basic distinguishing characteristics of different kinds of supernova (for example, having different mass progenitors or different stellar properties). Astronomers have therefore been at work trying to study these shocks. Unfortunately, supernovae are relatively rare, and so far only five supernovae have gone off in galaxies close enough to us, and recently enough, to have had their detailed shock properties studied.

CfA astronomers Atish Kamble and Alicia Soderberg and their colleagues have now measured a sixth. They been following SN2011dh in the radio since the explosion took place using a variety of radio telescope facilities, including very long baseline techniques, to obtain very high spatial resolution images of the shock. Observations they took 453 days after the event have now been combined with more recent measurements, enabling the scientists to determine the basic geometry of the shock: It has swept out a nearly spherical shell of hot material about 120 times larger in radius than the average distance Pluto is from the Sun.

Since the scientists know how long the shock has been propagating, about 453 days, they can estimate its velocity as about 19,000 kilometers per second (over forty-two million miles per hour). Combined with other observations of its radio brightness, the result implies that for nearly all of that time the expansion proceeded without being slowed down significantly by intervening material in space. Only about one-thousandth of a solar-mass of material has been swept up. These measurements are key tests of the robustness of theoretical predictions about supernovae and the underlying assumptions, and the results provide confidence in supernova shock theories. The research is part of an ongoing, cradle-to-grave study of this supernova.

Reference(s):

"Imaging the Expanding Shell of SN 2011dh," A. de Witt, M. F. Bietenholz, A. Kamble, A. M. Soderberg, A. Brunthaler, B. Zauderer, N. Bartel and M. P. Rupen, MNRAS, 455, 511, 2015.

Source: Smithsonian Astrophysical Observatory (SAO)