It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Tuesday, August 22, 2023
Spanish astronomer discovers new active galaxy
by Tomasz Nowakowski , Phys.org
Images of the newfound galaxy. Credit: Elio Quiroga Rodriguez (2023).
By analyzing the images of the Sombrero Galaxy obtained with the Hubble Space Telescope (HST), Elio Quiroga Rodriguez of the Mid Atlantic University in Spain, has identified a peculiar object, which turned out to be a galaxy hosting an active galactic nucleus (AGN). The finding was reported in a paper published August 11 on the pre-print server arXiv.
An AGN is a compact region at the center of a galaxy, more luminous than the surrounding galaxy light. Studies show that AGNs are very energetic due either to the presence of a black hole or star formation activity at the core of the galaxy.
Astronomers generally divide AGNs into two groups based on emission line features. Type 1 AGNs show broad and narrow emission lines, while only narrow emission lines are present in Type 2 AGNs. However, observations revealed that some AGNs transition between different spectral types; therefore, they were dubbed changing-look (CL) AGNs.
Sombrero Galaxy (also known as Messier 104 or NGC 4594) is an unbarred spiral galaxy located between the borders of the Virgo and Corvus constellations, some 31 million light years away. With a mass of about 800 billion solar masses, it is one of the most massive objects in the Virgo galaxy cluster. It also hosts a rich system of globular clusters.
Rodriguez has recently investigated HST images of the Sombrero Galaxy, focusing one particular object in its halo. He found that this object, previously classified as a globular cluster candidate, may be a barred spiral galaxy of the SBc type, with an AGN at its center.
"While studying HST images available on the HST Legacy website of the halo of M104 (HST proposal 9714, PI: Keith Noll), the author observed at 12:40:07.829-11:36:47.38 (in j2000) an object about four arcseconds in diameter. A study with VO tools suggests that the object is a SBc galaxy with AGN (Seyfert)," the paper reads.
The object is cataloged in the Pan-STARRS1 data archive as PSO J190.0326-11.6132. By analyzing the data from the Aladin Sky Atlas RGB Rodriguez found that PSO J190.0326-11.6132 is a galaxy with a dominant central arm, nucleus and possibly two spiral arms with hot young stars and dust. The astronomer proposes that the newfound galaxy should be named the "Iris Galaxy."
The study found that PSO J190.0326-11.6132 has a radial velocity at a level of 1,359 km/s. Rodriguez assumes that the object, if gravitationally bound to the Sombrero Galaxy, could be its satellite with an angular size of around 1,000 light years.
However, the author of the paper noted that if the Iris Galaxy is not associated with the Sombrero Galaxy, its distance may be some 65 million light years. In this scenario, the angular size of the newly detected should be about 71,000 light years.
The X-ray emission luminosity of the Iris Galaxy was measured to be approximately 18 tredecillion erg/s, assuming a distance of 65 million light years. Such luminosity indicates the presence of an active galactic nucleus, however further observations are required in order to determine whether this is a Type 1 or Type 2 AGN.
Cosmological redshift depends upon a galaxy's distance. Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)
In 1929 Edwin Hubble published the first solid evidence that the universe is expanding. Drawing upon data from Vesto Slipher and Henrietta Leavitt, Hubble demonstrated a correlation between galactic distance and redshift. The more distant a galaxy was, the more its light appeared shifted to the red end of the spectrum.
We now know this is due to cosmic expansion. Space itself is expanding, which makes distant galaxies appear to recede away from us. The rate of this expansion is known as the Hubble parameter, and while we have a good idea of its value, there is still a bit of tension between different results.
One of the difficulties in resolving this tension is that thus far we can only measure cosmic expansion as it appears right now. This also means we can't determine whether cosmic expansion is due to general relativity or a more subtle extension of Einstein's model. But as powerful new telescopes are built, we might be able to observe the evolution of cosmic expansion thanks to what is known as the redshift drift effect.
The Hubble parameter has a value of about 70 km/s per megaparsec. This means if a galaxy is about 1 megaparsec away (about 3 million light-years), then the galaxy appears to be moving away from us at about 70 km/s. If a galaxy is 2 megaparsecs away, it will appear to recede at about 140 km/s. The greater a galaxy's distance, the greater its apparent speed.
Since the universe is still expanding, with each passing year a galaxy is a bit more distant, and that means its redshift should become slightly larger. In other words, cosmic expansion means that the redshifts of galaxies should drift more to the red over time.
Theoretical redshift drift based on the standard model. Credit: ESO / ELT Science Case
This drift is extremely small. For a galaxy 12 billion light-years away, its apparent speed would be about 95% of the speed of light, while its drift would be just 15 cm/s each year. That's much too small for current telescopes to observe. But when the Extremely Large Telescope (ELT) starts gathering data in 2027, it should be able to observe this drift in time. Estimates are that after 5–10 years of precise observations, ELT should be able to see redshift drifts on the order of 5 cm/s.
While this will become a powerful tool in our understanding of the universe, it will take a lot of data and a lot of time. So a new paper, published on the preprint server arXiv, proposes a different method using gravitational lensing.
The authors call this effect redshift difference. Rather than observing the redshift of a galaxy over decades, the team proposes looking for distant galaxies that are gravitationally lensed by a closer galaxy. Lots of distant galaxies are lensed by a closer galaxy between us and the distant one, but most lensed galaxies appear as a single distorted arc to the side of the foreground galaxy.
How gravitational lensing can create multiple galaxy images. Credit: NASA/CXC/M.Weiss
But sometimes gravitational lensing can create multiple images of a distant galaxy. Since each image of the distant galaxy takes a slightly different path to reach us, the distance of each path is also slightly different. So instead of waiting decades for a galaxy to move farther away from us, we can get snapshots of the galaxy separated by years or decades. Each image would have a slightly different redshift, and by comparing these we could measure the redshift drift.
This is still beyond our current ability to detect. But while we are waiting for telescopes such as the ELT to come online, we can search for distant lensed galaxies with multiple images. That way when we do have the ability to detect redshift drift, we won't have to wait decades for the result.
More information: Chengyi Wang et al, The Redshift Difference in Gravitational Lensed Systems: A Novel Probe of Cosmology, arXiv (2023). DOI: 10.48550/arxiv.2308.07529
Fulvio Melia, Definitive test of theRh = ctuniverse using redshift drift, Monthly Notices of the Royal Astronomical Society: Letters (2016). DOI: 10.1093/mnrasl/slw157
New images from NASA’s James Webb Space Telescope of the well-known Ring Nebula provide unprecedented spatial resolution and spectral sensitivity. In the NIRCam (Near-Infrared Camera) image on the left, the intricate details of the filament structure of the inner ring are particularly visible in this dataset. On the right, the MIRI (Mid-InfraRed Instrument) image reveals particular details in the concentric features in the outer regions of the nebulae’s ring. Credit: ESA/Webb, NASA, CSA, M. Barlow (University College London), N. Cox (ACRI-ST), R. Wesson (Cardiff University).
NASA's James Webb Space Telescope obtained images of the Ring Nebula, one of the best-known examples of a planetary nebula. Much like the Southern Ring Nebula, one of Webb's first images, the Ring Nebula displays intricate structures of the final stages of a dying star. Roger Wesson from Cardiff University tells us more about this phase of a sun-like star's stellar lifecycle and how Webb observations have given him and his colleagues valuable insights into the formation and evolution of these objects, hinting at a key role for binary companions.
"Planetary nebulae were once thought to be simple, round objects with a single dying star at the center. They were named for their fuzzy, planet-like appearance through small telescopes. Only a few thousand years ago, that star was still a red giant that was shedding most of its mass."
"As a last farewell, the hot core now ionizes, or heats up, this expelled gas, and the nebula responds with colorful emission of light. Modern observations, though, show that most planetary nebulae display breathtaking complexity. It begs the question: how does a spherical star create such intricate and delicate non-spherical structures?"
"The Ring Nebula is an ideal target to unravel some of the mysteries of planetary nebulae. It is nearby, approximately 2,200 light-years away, and bright—visible with binoculars on a clear summer evening from the northern hemisphere and much of the southern. Our team, named the ESSENcE (Evolved StarS and their Nebulae in the JWST Era) team, is an international group of experts on planetary nebulae and related objects."
"We realized that Webb observations would provide us with invaluable insights, since the Ring Nebula fits nicely in the field of view of Webb's NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) instruments, allowing us to study it in unprecedented spatial detail. Our proposal to observe it was accepted (General Observers program 1558), and Webb captured images of the Ring Nebula just a few weeks after science operations started on July 12, 2022."
"When we first saw the images, we were stunned by the amount of detail in them. The bright ring that gives the nebula its name is composed of about 20,000 individual clumps of dense molecular hydrogen gas, each of them about as massive as the Earth. Within the ring, there is a narrow band of emission from polycyclic aromatic hydrocarbons, or PAHs—complex carbon-bearing molecules that we would not expect to form in the Ring Nebula."
"Outside the bright ring, we see curious 'spikes' pointing directly away from the central star, which are prominent in the infrared but were only very faintly visible in Hubble Space Telescope images. We think these could be due to molecules that can form in the shadows of the densest parts of the ring, where they are shielded from the direct, intense radiation from the hot central star."
"Our MIRI images provided us with the sharpest and clearest view yet of the faint molecular halo outside the bright ring. A surprising revelation was the presence of up to ten regularly-spaced, concentric features within this faint halo. These arcs must have formed about every 280 years as the central star was shedding its outer layers. When a single star evolves into a planetary nebula, there is no process that we know of that has that kind of time period."
"Instead, these rings suggest that there must be a companion star in the system, orbiting about as far away from the central star as Pluto does from our sun. As the dying star was throwing off its atmosphere, the companion star shaped the outflow and sculpted it. No previous telescope had the sensitivity and the spatial resolution to uncover this subtle effect."
"So how did a spherical star form such a structured and complicated nebulae as the Ring Nebula? A little help from a binary companion may well be part of the answer."
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