Astronomers using the Southern African Large Telescope (SALT), have measured the rotation of some of the largest spiral galaxies, spinning at up to 570 kilometres per second! Their rapid spin is a result of sitting within an extraordinarily massive cloud, or halo, of dark matter – invisible matter detectable only through its gravity. The largest “super spiral” studied here resides in a dark matter halo weighing at least 40 trillion times the mass of our Sun. 

When it comes to galaxies, how fast is fast? The Milky Way, an average spiral galaxy, spins at a speed of 210 kilometres per second in our Sun’s neighbourhood. New research has found that the most massive spiral galaxies spin faster than expected. These “super spirals,” the largest of which weigh about 20 times more than our Milky Way, spin at a rate of up to 570 kilometres per second.

Super spirals are exceptional in almost every way. In addition to being much more massive than the Milky Way, they’re also brighter and larger in physical size. The largest span 450,000 light-years compared to the Milky Way’s 100,000-light-year diameter. Only about 100 super spirals are known to date. Super spirals were discovered as an important new class of galaxies while studying data from the Sloan Digital Sky Survey as well as the NASA/IPAC Extragalactic Database (NED).

“Super spirals are extreme by many measures,” says Patrick Ogle of the Space Telescope Science Institute in Baltimore, Maryland. “They break the records for rotation speeds.”

Ogle is the first author of a paper that was published October 10, 2019, in the Astrophysical Journal Letters. The paper presents new data on the rotation rates of super spirals collected with the Southern African Large Telescope (SALT), the largest single optical telescope in the southern hemisphere. Additional data were obtained using the 5-meter Hale telescope of the Palomar Observatory, operated by the California Institute of Technology. Data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission was crucial for measuring the galaxy masses in stars and star formation rates.

“This work beautifully illustrates the powerful synergy between optical and infrared observations of galaxies, revealing stellar motions with SDSS and SALT spectroscopy, and other stellar properties — notably the stellar mass or ‘backbone’ of the host galaxies — through the WISE mid-infrared imaging,” says Tom Jarrett of the University of Cape Town, South Africa.

Theory suggests that super spirals spin rapidly because they are located within incredibly large clouds, or halos, of dark matter. Dark matter has been linked to galaxy rotation for decades. Astronomer Vera Rubin pioneered work on galaxy rotation rates, showing that spiral galaxies rotate faster than if their gravity were solely due to the constituent stars and gas. An additional, invisible substance known as dark matter must influence galaxy rotation. A spiral galaxy of a given mass in stars is expected to rotate at a certain speed. Ogle’s team finds that super spirals significantly exceed the expected rotation rate.

Super spirals also reside in larger than average dark matter halos. The most massive halo that Ogle measured contains enough dark matter to weigh at least 40 trillion times as much as our Sun. That amount of dark matter would normally contain a group of galaxies rather than a single galaxy.

“It appears that the spin of a galaxy is set by the mass of its dark matter halo,” Ogle explains.

The fact that super spirals break the usual relationship between galaxy mass in stars and rotation rate is a new piece of evidence against an alternative theory of gravity known as Modified Newtonian Dynamics, or MOND. MOND proposes that on the largest scales like galaxies and galaxy clusters, gravity is slightly stronger than would be predicted by Newton or Einstein. This would cause the outer regions of a spiral galaxy, for example, to spin faster than otherwise expected based on its mass in stars. MOND is designed to reproduce the standard relationship in spiral rotation rates, therefore it cannot explain outliers like super spirals. The super spiral observations suggest no non-Newtonian dynamics is required.

Despite being the most massive spiral galaxies in the universe, super spirals are actually underweight in stars compared to what would be expected for the amount of dark matter they contain. This suggests that the sheer amount of dark matter inhibits star formation. There are two possible causes: 1) Any additional gas that is pulled into the galaxy crashes together and heats up, preventing it from cooling down and forming stars, or 2) The fast spin of the galaxy makes it harder for gas clouds to collapse against the influence of centrifugal force.

“This is the first time we’ve found spiral galaxies that are as big as they can ever get,” Ogle says.

Despite these disruptive influences, super spirals are still able to form stars. Although the largest elliptical galaxies formed all or most of their stars more than 10 billion years ago, super spirals are still forming stars today. They convert about 30 times the mass of the Sun into stars every year, which is normal for a galaxy of that size. By comparison, our Milky Way forms about one solar mass of stars per year.

Ogle and his team have proposed additional observations to help answer key questions about super spirals, including observations designed to better study the motion of gas and stars within their disks. After its 2021 launch, NASA’s James Webb Space Telescope could study super spirals at greater distances and correspondingly younger ages to learn how they evolve over time. And NASA’s WFIRST mission may help locate more super spirals, which are exceedingly rare, thanks to its large field of view.

The Space Telescope Science Institute is expanding the frontiers of space astronomy by hosting the science operations centre of the Hubble Space Telescope, the science and operations centre for the James Webb Space Telescope, and the science operations centre for the future Wide Field Infrared Survey Telescope (WFIRST). STScI also houses the Mikulski Archive for Space Telescopes (MAST) which is a NASA-funded project to support and provide to the astronomical community a variety of astronomical data archives and is the data repository for the Hubble, Webb, Kepler, K2, TESS missions and more.

Notes for Editors:

“A Break in Spiral Galaxy Scaling Relations at the Upper Limit of Galaxy Mass” by Ogle, P.M .et. al. is published in the Astrophysical Journal Letters.

Ogle, P. M.; Jarrett, T; Lanz, L.; … (and 4 authors from 4 institutions), 2019/10. A Break in Spiral Galaxy Scaling Relations at the Upper Limit of Galaxy Mass. Astrophys. J. Letters., 884. https://ui.adsabs.harvard.edu/abs/2019ApJ…884L..11O/abstract

Image Caption:
The top row of this mosaic features Hubble images of three spiral galaxies, each of which weighs several times as much as the Milky Way. The bottom row shows three even more massive spiral galaxies that qualify as “super spirals,” which were observed by the ground-based Sloan Digital Sky Survey. Super spirals typically have 10 to 20 times the mass of the Milky Way. The galaxy at lower right, 2MFGC 08638, is the most massive super spiral known to date, with a dark matter halo weighing at least 40 trillion Suns.
Image Credits: Top row: NASA, ESA, P. Ogle and J. DePasquale (STScI). Bottom row: SDSS, P. Ogle and J. DePasquale (STScI)

The Southern African Large Telescope

The Southern African Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere and among the largest in the world. It has a hexagonal primary mirror array 11 metres across, comprising 91 individual 1m hexagonal mirrors.

SALT is situated at the South African Astronomical Observatory (SAAO) field station near the small town of Sutherland, in the Northern Cape province, about 400 km from Cape Town. SALT is funded by a consortium of international partners from South Africa, the United States, Germany, Poland, India, the United Kingdom and New Zealand. The telescope has been in full science operation since 2011 and is realising its huge potential as Africa’s Giant Eye on the Universe.

South African Astronomical Observatory

Founded in 1820, the South African Astronomical Observatory (SAAO; www.saao.ac.za) is the national centre for optical and infrared astronomy in South Africa. Its primary role is to conduct fundamental research in astronomy and astrophysics by providing a world-class facility to scientists. The SAAO also promotes astronomy and astrophysics in Southern Africa, by sharing research findings and discoveries, and participating in outreach activities to enthuse citizens about physics and astronomy. The SAAO is a facility of the National Research Foundation, which operates under the South African Department of Science and Technology. The SAAO encompasses headquarters in the eponymous suburb of Observatory in Cape Town, and a dedicated research and observation station with several working telescopes (including SALT; www.salt.ac.za) outside the Karoo town of Sutherland in the Northern Cape.

For more information, please contact:

Daniel Cunnama
South African Astronomical Observatory
Cape Town, South Africa
Email: daniel@saao.ac.za

Researchers from the South African Astronomical Observatory (SAAO) have utilised the South African Radio Astronomy Observatory MeerKAT Telescope to confirm the existence of a never-before-seen flaring black hole.

The European Space Agency’s (ESA) XMM-Newton X-Ray space telescope recently discovered mysterious X-ray flashes from the active black hole at the core of the galaxy GSN 069, some 250 million light-years away. 

On 24 December 2018, the object was seen to suddenly increase its brightness by up to a hundred times, then dimmed back to its normal levels within one hour and lit up again nine hours later. 

“It was completely unexpected,” says Giovanni Miniutti, of the Centro de Astrobiología in Madrid, Spain, lead author of a new paper published in the prestigious journal, Nature, today. 

“Giant black holes regularly flicker like a candle but the rapid, repeating changes seen in GSN 069 from December onwards are something completely new.”

“The X-ray emission comes from material that is being accreted into the black hole and heats up in the process,” explains Giovanni. 

Although never before observed, Giovanni and colleagues think periodic flares like these might actually be quite common in the Universe. It is possible that the phenomenon hadn’t been identified before because most black holes at the cores of distant galaxies, with masses millions to billions of times the mass of our Sun, are much larger than the one in GSN 069, which weighs about 400,000 times our Sun. 

In order to study the radio properties of the source of these X-ray flashes, astronomers from the South African Astronomical Observatory (SAAO) used the powerful new capabilities provided by their fellow National Research Foundation (NRF) Facility, the South African Radio Astronomy Observatory (SARAO).

SAAO Astronomer’s Dr Retha Pretorius and Dr Itumeleng Monageng utilised SARAO’s MeerKAT Radio telescope and were able to detect the black hole at lower frequencies (1.3GHz) to complement other radio observations from ATCA (5.5 and 9 GHz) and VLA (6 GHz).

“Having access to such a powerful radio telescope has enabled us to compete internationally on major discoveries like this, MeerKAT is yet another world-class telescope available to South African astronomers” said Dr Monageng.

SARAO Director Rob Adam added “It’s exciting to see MeerKAT being used in a groundbreaking multi-wavelength study by young South African researchers from our sister observatory”

 

Notes to editors

“Nine hour X-ray quasi-periodic eruptions from a low mass black hole galactic nucleus,” by G. Miniutti et al. is published in Nature https://www.nature.com/articles/s41586-019-1556-x

The international research team used astronomical data from ESA’s XMM-Newton, NASA’s Chandra and Swift X-ray observatories, the NASA/ESA Hubble Space Telescope, NRAO’s Karl G. Jansky Very Large Array in New Mexico, USA, CSIRO’s Australia Telescope Compact Array in Australia, and SARAO’s MeerKAT radio telescope in South Africa. 

South African Astronomical Observatory 

Founded in 1820, the South African Astronomical Observatory (SAAO; www.saao.ac.za) is the national centre for optical and infrared astronomy in South Africa. Its primary role is to conduct fundamental research in astronomy and astrophysics by providing a world-class facility to scientists. The SAAO also promotes astronomy and astrophysics in Southern Africa, by sharing research findings and discoveries, and participating in outreach activities to enthuse citizens about physics and astronomy. The SAAO is a facility of the National Research Foundation, which operates under the South African Department of Science and Technology. The SAAO encompasses headquarters in the eponymous suburb of Observatory in Cape Town, and a dedicated research and observation station with several working telescopes (including SALT; www.salt.ac.za) outside the Karoo town of Sutherland in the Northern Cape.

MeerKAT 

MeerKAT, originally the Karoo Array Telescope, is a radio telescope inaugurated in 2018 consisting of 64 antennas spread over a diameter of eight kilometers in the Northern Cape province of South Africa. It is the most sensitive telescope of its kind in the world and is a precursor to the Square Kilometre Array (SKA) radio telescope, to be built in South Africa and Australia within the coming decade.

The South African Radio Astronomy Observatory

The South African Radio Astronomy Observatory (SARAO), a facility of the National Research Foundation, is responsible for managing all radio astronomy initiatives and facilities in South Africa, including the MeerKAT radio telescope in the Karoo, and the Geodesy and VLBI activities at the HartRAO facility. SARAO also coordinates the African Very Long Baseline Interferometry Network (AVN) for the eight SKA partner countries in Africa, as well as South Africa’s contribution to the infrastructure and engineering planning for the Square Kilometre Array radio telescope. To maximise the return on South Africa’s investment in radio astronomy, SARAO is managing programmes to create capacity in radio astronomy science and engineering research, and the technical capacity required to support site operations.

 

For more information, please contact:

Daniel Cunnama

South African Astronomical Observatory

Cape Town, South Africa

Email: daniel@saao.ac.za

 

Giovanni Miniutti

Centro de Astrobiología

Madrid, Spain
Email: gminiutti@cab.inta-csic.es

The South African Astronomical Observatory’s 1.0m telescope provided crucial follow-up observations in new research published today by members of the Astronomy and Astrophysics Group at the University of Warwick, UK, detailing the discovery of an exoplanet in the so-called “Neptunian Desert”.

The planet NGTS-4b, also nick-named ‘The Forbidden Planet’ by researchers is about 20 times the mass of the Earth and about 3 times the size. The planet orbits its host star in just 1.3 days with temperatures exceeding 1000 degrees Celsius.

NGTS-4b was first noticed using the state-of-the-art Next-Generation Transit Survey (NGTS) observing facility, designed to search for transiting planets on bright stars. NGTS is situated at the European Southern Observatory’s Paranal Observatory in the heart of the Atacama Desert, Chile.

The discovery relied heavily on follow-up observations made by Dr Matt Burleigh (University of Leicester) using the Sutherland High-speed Optical Cameras (SHOC) on the SAAO 1.0m Telescope in November 2017. This triggered an international effort to obtain further observations and a few weeks later it was confirmed that the transit was indeed a sub-Neptune exoplanet.

When looking for new planets astronomers look for a dip in the light of a star – this is the planet orbiting it and blocking the light. Usually, only dips of greater than 1% are picked up by ground-based searches, but the NGTS telescopes can pick up a dip of just 0.1%. With a dip almost that small, this exoplanet is, by a long way, the shallowest transiting planet ever discovered by a ground-based survey (the transit is less than 0.2%).

Dr Burleigh explained “Since this transit is so shallow, NGTS-4b wasn’t initially one of our top priority targets. But thanks to the excellent telescopes at SAAO in Sutherland, we were able to detect and confirm the transit, convincing ourselves the planet is real. We then set in motion many more observations to measure its mass and size.”

It is the first exoplanet of its kind to have been found in the Neptunian Desert, which is the region close to stars where, up until now, no Neptune-sized planets have been found. This area receives strong irradiation from the star, meaning the planets do not retain their gaseous atmosphere as they evaporate leaving just a rocky core. However, NGTS-4b still has its atmosphere of gas leading researchers to believe the planet may have moved into the Neptunian Desert recently, in the last
one million years or that it was originally very big and the atmosphere is still evaporating.

High-res image available at https://warwick.ac.uk/services/communications/medialibrary/images/may2019/exoplanet_ngts-4b_-_v4.jpg
The full paper at https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stz1084/5475662

South Africa is looking forward to hosting the International Astronomical Union (IAU) General Assembly in 2024 — the first on the African continent. The meeting will come at a time of burgeoning scientific prosperity for the growing community of indigenous South African and African astronomers.

SAAO Astronomer, David Buckley, today published an article in the prestigious Nature Astronomy journal on the changing landscape of South African astronomy, highlighting the huge strides made in the development of astronomy in South Africa and the continent as a whole in recent decades, and providing some perspectives on the future of astronomy on the continent:

“the African continent has seen enormous strides in astronomy development over the last ~2 decades, not least being the construction of three major internationally recognized facilities. First came the European-led High Energy Stereoscopic System (HESS), a ground-based Cherenkov TeV gamma-ray telescope array in Namibia, which began operations in 2002. The 10-m class Southern African Large Telescope (SALT), still, the largest single optical telescope in the Southern Hemisphere, was completed in 2005 and is situated at the Sutherland site of the South African Astronomical Observatory (SAAO), which itself was established in 1972. Finally, the MeerKAT radio telescope array situated near the remote Karoo town of Carnarvon, one of the Square Kilometre Array (SKA) pathfinders and now a precursor to SKA Phase 1, was inaugurated only a month before the IAU General Assembly, in July 2018.”

Read the full article here:  https://rdcu.be/bAxLO

On the 1st of January 2019, NASA’s New Horizon’s spacecraft performed a very exciting flyby of the most distant object ever explored, 2014 MU69, nicknamed Ultima Thule. MU69 is located in the Kuiper belt, the icy disk in the outer solar system that contains leftover material from the formation of the Solar System 4.5 billion years ago. In order to prepare for this flyby, and learn as much as possible about this object, astronomers at SAAO and around the world have been performing Earth-based observations from as early as 2017.

The New Horizons spacecraft, which initially visited Pluto in 2015, was then re-directed to explore an even more distant object. For this, scientists chose MU69, a body around 30km in size in the outer reaches of our solar system, and aimed to learn about its surface composition, its structure, and whether it hosts moonlets, a coma, or rings.MU69 offered a rare opportunity to learn more about objects in our outer solar system and how they may have formed.

However long before the 2019 flyby, observations of MU69 had already begun. Astronomers, using what are known as occultation observations, had already learned a fair amount about 2014 MU69. An occultation observation is performed as the object in question moved in front of a background star, briefly blocking the star’s light:

In a recently published study led by Eliot Young (Southwest Research Institute), and including SAAO Astronomers, scientists searched for evidence of rings around MU69 using these occultation observations. Observations were performed on three dates in 2017: on 3 June, from SAAO and Argentina, on 10 June, from the airborne observatory SOFIA, and on 17 July, from Argentina. On these days, telescopes were set up with the goal of catching 2014 MU69 as it crossed in front of a background star.

The authors compared predicted light curves to the actual dimming of the background star captured during MU69’s occultations and concluded that MU69 was highly unlikely to host any rings. This lack of rings is consistent with the newly obtained low-resolution images from New Horizons’s flyby.

Citation
“Limits on a Ring System at 2014 MU69 from Recent Stellar Occultations,” Eliot F. Young et al 2018 Res. Notes AAS 2 224. https://doi.org/10.3847/2515-5172/aaf574

Links:

Occultations Suggest No Rings for Ultima Thule

Original Publication:

Young2018RNAAS2.224

Stellar occultations are a powerful technique that allows characterization of foreground objects by watching them block light from a distant star. This technique is particularly useful for studying small and/or distant objects in the Solar System, which are difficult to see from the ground. In March 2017, a team of astronomers from the South African Astronomical Observatory and the Massachusetts Institute of Technology observed a stellar occultation that was predicted for the large, Trans-Neptunian Object (TNO) Orcus (Fig. 1, left).

Prior to this observation, Orcus was known to be approximately 900 km in size and had one satellite, Vanth, with a size of roughly 280 km. The Orcus system is in a 3:2 orbital resonance with Neptune, similar to Pluto’s orbit. Although not expected to maintain an atmosphere, Orcus’ features could hint toward a possible resurfacing mechanism, such as cryovolcanism. Goals of the occultation observation included accurately constraining Orcus’ size, measuring any atmosphere around Orcus, and detecting rings or debris in the system.

Five sites in North America attempted the observation, with locations spanning from Chile to northern California. Two sites successfully detected the star disappearing: NASA’s 3-m Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai’i and a 1-m Las Cumbres Observatory (LCO) telescope at McDonald Observatory, Texas (Fig. 2). However, a quick analysis of the geometry and the timing showed that data did not align with the expectation of one star being occulted by one outer Solar System object. After months of careful study, the best guess was that one site observed an occultation by Vanth of the target star while the second site observed an occultation by Orcus of an unknown secondary star.

An external reviewer recommended obtaining high-resolution images in order to definitively solve the mystery. So, a proposal was submitted to the 8.1-m Gemini South telescope to observe the star using the Differential Speckle Survey Instrument (DSSI). The DSSI speckle images easily detected a companion star 250 milliarcsec away from the brighter primary (Fig. 3). Armed with confirmation of the location of the second star, the occultation data were reanalyzed to reveal that both detections were of Vanth, each blocking one of the two separate stars (Fig. 1, right).

The data allowed Vanth’s size to be measured at 443±10 km in diameter. They also placed a constraint of a few microbars on any global Vanth atmosphere and did not detect any material in the two star paths down to a limit of a few km in extent.

Click here for the Gemini Observatory press release, “Outer Solar System Object has Astronomers Seeing Double”.

Publication details:
“A Stellar Occultation by Vanth, a satellite of (90482) Orcus”
Amanda A. Sickafoose, Amanda S. Bosh Stephen E. Levine, Carlos A. Zuluaga, Anja Genade, Karsten Schindler, Tim Lister, and Michael J. Person
Icarus, volume 319, pages 657-668
https://doi.org/10.1016/j.icarus.2018.10.016

Preprint available at https://arxiv.org/abs/1810.08977.