by Paul Gilster | Apr 11, 2019 | Deep Sky Astronomy & Telescopes |
Messier 87, a massive elliptical galaxy in the Virgo cluster, is some 55 million light years from Earth, and even though the black hole at its center has a mass 6.5 billion times that of the Sun, it’s a relatively small object, about the size of our Solar System. Resolving an image of that black hole is, says the University of Arizona’s Dimitrios Psaltis, like “taking a picture of a doughnut placed on the surface of the moon.” But the M87 black hole is one of the largest we could see from Earth, making it a natural target for observations, in this case using radio telescopes working at a frequency of 230 GHz, corresponding to a wavelength of 1.3mm.
A decade ago, working with Avery Broderick, Harvard’s Avi Loeb highlighted the advantages of M87 as an observational target, finding it in many ways preferable to the black hole at the heart of our own Milky Way:
M87 provides a promising second target for the emerging millimeter and submillimeter VLBI capability. Its presence in the Northern sky simplifies its observation and results in better baseline coverage than available for Sgr A*. In addition, its large black hole mass, and correspondingly long dynamical timescale, makes possible the use of Earth aperture synthesis, even during periods of substantial variability.
That paper, “Imaging the Black Hole Silhouette of M87: Implications for Jet Formation and Black Hole Spin,” is worth revisiting (abstract), for those intrigued with how these observations get made and the kinds of things we can learn from them.
I was reminded, when I first saw the now famous image, of the nature of M87 itself. Elliptical galaxies, unlike our barred spiral Milky Way, show slow rates of star formation, their primary population being older stars, and as you would imagine, they contain little gas and dust, while also housing a large number of globular clusters. Back in 2012, I ran across a paper by Falguni Suthar and Christopher McKay (NASA Ames) assessing habitability in such galaxies. What an environment to set a science fiction story! Consider the image below before we cut to the black hole image that is now center stage in the news, because here’s the context:
Image: A composite of visible (or optical), radio, and X-ray data of the giant elliptical galaxy, M87. M87 lies at a distance of 55 million light years and is the largest galaxy in the Virgo cluster of galaxies. Bright jets moving at close to the speed of light are seen at all wavelengths coming from the massive black hole at the center of the galaxy. It has also been identified with the strong radio source, Virgo A, and is a powerful source of X-rays as it resides near the center of a hot, X-ray emitting cloud that extends over much of the Virgo cluster. The extended radio emission consists of plumes of fast-moving gas from the jets rising into the X-ray emitting cluster medium. Credit: X-ray: NASA/CXC/CfA/W. Forman et al.; Radio: NRAO/AUI/NSF/W. Cotton; Optical: NASA/ESA/Hubble Heritage Team (STScI/AURA), and R. Gendler.
Could life survive in environments like this? I bring this up again as background, but also because yesterday we looked at the question of hardy microorganisms and their ability to withstand high levels of X-ray and UV radiation. Here’s what McKay and Suthar said in 2012:
Complex life forms are sensitive to ionizing radiation and changes in atmospheric chemistry that might result. However, microbial life forms, e.g. Deinococcus radiodurans, can withstand high doses of radiation and are more ?exible in terms of atmospheric composition. Furthermore, microbial life in subsurface environments would be effectively shielded from space radiation. Thus, while a high level of radiation from nearby supernovae may be inimical to complex life, it would not extinguish microbial life.
It’s fascinating to me that we’ve begun studying such questions on a galactic scale. Fascinating too that we’re now peering into the heart of an active galaxy to reveal its powerhouse black hole. By now the image is familiar, but let’s see it again because it’s just extraordinary.
Image: Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. Credit: Event Horizon Telescope Collaboration.
One thing I saw little attention given to in the coverage was that the Event Horizon Telescope, which produced the image, was supplemented by work from spacecraft. Remember that the EHT is comprised of telescopes located around the surface of our planet, to produce a planet-scale interferometer capable of making such an observation. But the Chandra X-ray spacecraft was also involved, as was the Nuclear Spectroscopic Telescope Array (NuSTAR), and the Neil Gehrels Swift Observatory. All of these, working at X-ray wavelengths, observed the M87 black hole at the same time it was under study by the EHT in April of 2017.
I point to this because while the space assets could not image the black hole, data from them were used to measure the brightness of the M87 jet, particles driven by an enormous energy boost from the black hole itself and surging away from it at nearly the speed of light. The hope here is that X-rays can help us measure particle events near the event horizon to coordinate with the black hole images. Also involved in space was the Neutron star Interior Composition Explorer (NICER), a NASA experiment on the International Space Station that looked at the center of the Milky Way and the black hole known as Sgr A*. Part of the EHT’s mandate is to study the origin of jets like this one, so these extraordinary interactions now become visible.
As to the ground-based observatories of the EHT themselves, what an accomplishment! The international team involved totalled over 200 astronomers, whose work is presented in a special issue of Astrophysical Journal Letters. In the black hole work, the EHT used an array of eight radio telescopes with worldwide coverage, from the Antarctic to Spain, Chile and Hawaii, all located in high-altitude settings where conditions are ideal for observation.
Jonathan Weintroub (CfA) coordinates the EHT’s Instrument Development Group:
“The resolution of the EHT depends on the separation between the telescopes, termed the baseline, as well as the short millimeter radio wavelengths observed. The finest resolution in the EHT comes from the longest baseline, which for M87 stretches from Hawai’i to Spain. To optimize the long baseline sensitivity, making detections possible, we developed a specialized system which adds together the signals from all available SMA dishes on Maunakea. In this mode, the SMA acts as a single EHT station.”
Spectacular. The very long baseline interferometry creates a virtual dish that is planet-sized, able to resolve an object to 20 micro-arcseconds. Working with a conjunction of four nights that would produce clear seeing for all eight observatories, the telescopes took in massive amounts of data — 5,000 trillion bytes of data in all — saved on 1,000 storage disks. Transmitting all that information for subsequent processing was ruled out, for air transport from FedEx could take the hard disks onto which the data had been recorded to a single location much faster. These are signals that needed to be aligned within trillionths of a second to achieve a valid result.
The resulting imagery is the payoff. The central dark region is surrounded by a ring of light, as Einstein’s equations led scientists to expect. We can’t, of course, see the black hole itself, but plasma emitted from its accretion disk, where matter piles up as material falls into the black hole, is heated to billions of degrees and accelerated almost to lightspeed. We get an image of the black hole’s shadow’ that is about 2.5 times larger than the event horizon. M87’s event horizon is thought to be some 25 billion miles across, making it 3 times the size of Pluto’s orbit.
“Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well,“ said Luciano Rezzolla, professor for theoretical astrophysics at Goethe University and a researcher on the EHT. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.“
Image: This artist’s impression depicts the paths of photons in the vicinity of a black hole. The gravitational bending and capture of light by the event horizon is the cause of the shadow captured by the Event Horizon Telescope. Credit: Nicolle R. Fuller/NSF.
This is a black hole massive enough that a planet orbiting it could move around it within a week while traveling, says MIT’s Geoffrey Crew, close to the speed of light. Crew’s colleague Vincent Fish, also at MIT’s Haystack Observatory, amplifies on the point:
“People tend to view the sky as something static, that things don’t change in the heavens, or if they do, it’s on timescales that are longer than a human lifetime. But what we find for M87 is, at the very fine detail we have, objects change on the timescale of days. In the future, we can perhaps produce movies of these sources. Today we’re seeing the starting frames.”
Now that’s something worth waiting for, movies of the accretion disk caught in the tortured spacetime of a galaxy’s central black hole. M87 anchors a jet stretching tens of thousands of light years, so we’re talking about seeing the dynamics of the jet’s interactions with the black hole. Fine-tuning EHT methods and expanding its sites points in the direction of further breakthrough imagery.
But what an accomplishment we’ve already achieved via instruments all over the world — ALMA and APEX in Chile, the IRAM 30 meter telescope in Spain, the James Clerk Maxwell telescope and the Submillimeter Array (both in Hawaii), the Large Millimeter Telescope (LMT) in Mexico, the Submillimeter Telescope (SMT) in Arizona and the South Pole Telescope (SPT) in Antarctica.
The papers are The Event Horizon Telescope Collaboration et al., “First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole,” Astrophysical Journal Letters Vol. 875, No. 1 (10 April 2019) (abstract); and from the same issue: “First M87 Event Horizon Telescope Results. II. Array and Instrumentation” (abstract); “First M87 Event Horizon Telescope Results. III. Data Processing and Calibration” (abstract); “First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole” (abstract); “First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring” (abstract); and “First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole” (abstract). The paper on M87 and galactic habitability is Suthar & McKay, “The Galactic Habitable Zone in Elliptical Galaxies,” International Journal of Astrobiology, published online 16 February 2012 (abstract).
by Paul Gilster | Apr 10, 2019 | Exoplanetary Science |
With 250 times more X-ray radiation than Earth receives and high levels of ultraviolet, would Proxima b, that tantalizing, Earth-sized world around the nearest star, have any chance for habitability? The answer, according to Jack O’Malley-James and Lisa Kaltenegger (Cornell University) is yes, and in fact, the duo argue that life under these conditions could deploy a number of possible strategies for dealing with the radiation influx. Their conclusions appear in a new paper in Monthly Notices of the Royal Astronomical Society.
Kaltenegger is director of Cornell’s Carl Sagan Institute, where O’Malley-James serves as a research associate. Modeling surface environments on four exoplanets that are prone to frequent flares — Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b — Kaltenegger and O’Malley-James examined different atmospheric solutions that could suppress UV damage in living cells.
Thin atmospheres and a lack of ozone protection fail to block UV radiation well, no surprise there, and such atmospheres do not measure up favorably when compared to atmospheres like that of the Earth today. But go back four billion years and we find that the modeled planets receive radiation in the UV significantly lower than what the Earth experienced in that era of its development. Earth was at that time uninhabitable by human standards — had any humans been available — but life had indeed emerged and continued to thrive. Thus the authors write that UV radiation “…should not be a limiting factor for the habitability of planets orbiting M stars.”
Image: The intense radiation environments around nearby M stars could favor habitable worlds resembling younger versions of Earth. Credit: Jack O’Malley-James/Cornell University.
The extremophile Deinococcus radiodurans is key to this study, for it is one of the most radiation-resistant organisms known. By varying the UV wavelengths, the scientists assessed the mortality rates of the organism, in which it becomes clear that some wavelengths of UV are more damaging to biological molecules than others. From the paper:
…we use this as a benchmark against which to compare the habitability of the different radiation models. This action spectrum compares the effectiveness of different wavelengths of UV radiation at inducing a 90 per?cent mortality rate. It highlights which wavelengths have the most damaging irradiation for biological molecules: for example, the action spectrum in Fig. 4 shows that a dosage of UV radiation at 360?nm would need to be three orders of magnitude higher than a dosage of radiation at 260?nm to produce similar mortality rates in a population of this organism.
Image: This is Figure 4 from the paper. Caption: Relative biological effectiveness of UV surface radiation on Proxima-b. (A) The biological effectiveness of UV on DNA and the radiation-resistant microorganism D. radiodurans (Voet et al. 1963; Diffey 1991) quantifies the relative effectiveness of different wavelengths of UV radiation to cause DNA destruction or, for D. radiodurans, mortality, which increases with decreasing wavelength. Biological effectiveness of UV damage for (B) oxygenic atmospheres and (C) anoxic atmosphere models shown as convolution of the surface UV flux and action spectrum over wavelength (solid line shows flaring, dashed line quiescent star), compared to present-day Earth (red solid) and early Earth (3.9 billion years ago) (red dashed). Credit: Lisa Kaltenegger/Jack O’Malley-James/Cornell University.
We can’t rule out organisms below ground or living in water or rock, not to mention such survival characteristics as biofluorescence or protective pigments. We know of microorganisms that can tolerate full solar UV in space exposure experiments, using protective cells or pigments as effective UV screens. Biofluorescence offers protection against radiation because UV can be upshifted to longer wavelengths that produce less harm. The authors think protective biofluorescence would be at its most useful during the intense UV flux of flares, although a constant level of high UV might produce continuous fluorescence.
Here we have a potential biosignature, cited by the authors in a previous paper:
Because biofluorescence is independent of the visible flux of the host star and only dependent on the UV flux of the star, emitted biofluorescence can increase the visible flux of a planet orbiting an active M-star by several orders of magnitude (O’Malley-James & Kaltenegger 2018) during a flare.
We may get our first look at such atmospheres by observing ozone, which is potentially detectable by the James Webb Space Telescope. On the other hand, a high-enough level of UV could also produce a biosphere below ground that would present, if any, only the weakest of biosignatures. Even so, the authors conclude that nearby planets around M-dwarfs like those studied here are serious candidates for biosignature examination by future observatories.
While a multitude of factors ultimately determine an individual planet’s habitability our results demonstrate that high UV radiation levels may not be a limiting factor. The compositions of the atmospheres of our nearest habitable exoplanets are currently unknown; however, if the atmospheres of these worlds resemble the composition of Earth’s atmosphere through geological time, UV surface radiation would not be a limiting factor to the ability of these planets to host life. Even for planets with eroded or anoxic atmospheres orbiting active, flaring M stars the surface UV radiation in our models remains below that of the early Earth for all cases modelled. Therefore, rather than ruling these worlds out in our search for life, they provide an intriguing environment for the search for life and even for searching for alternative biosignatures that could exist under high-UV surface conditions.
The paper is O’Malley-James & Kaltenegger, “Lessons from early Earth: UV surface radiation should not limit the habitability of active M star systems,” Monthly Notices of the Royal Astronomical Society Vol. 485 Issue 4 (June 2019), pp. 5598-5603 (full text).
by Paul Gilster | Apr 9, 2019 | Outer Solar System |
You’ll recall that well before New Horizons completed its primary mission at Pluto/Charon, the search was on for a Kuiper Belt Object that could serve as its next destination. Eventually we found Ultima Thule (2014 MU-69), from which priceless data were gathered at the beginning of January. Finding the target wasn’t easy given the distances involved and the small size of the relevant objects, which is why the Hubble Space Telescope was brought into the search.
The starfield in Sagittarius is crowded as we look toward galactic center, but despite the efforts of both the 8.2-meter Subaru telescope in Hawaii and the 6.5-meter Magellan telescopes in Chile, no KBOs among those found were within range of New Horizons. It was Hubble that made the difference, and Hubble which will presumably return a second target, if indeed the New Horizons team is granted an extended mission that can reach it. It’s worth noting, too, that it was Hubble that helped New Horizons in its discovery of Pluto’s smaller four moons, while also performing searches of the system for any dust rings that could harm the mission.
KBOs have never been heated by the Sun, so they provide the most pristine sample available of the earliest days of system formation. What we’ve learned about the Kuiper Belt so far is that there are a large number of binary objects within it, and as Southwest Research Institute scientist Alex Parker notes, many of these consist of two objects of similar mass. Parker will lead a new survey on the Kuiper Belt awarded to SwRI by the Space Telescope Science Institute (STScI), one that will put the emphasis on characterizing these binary populations.
“These binary systems are powerful tracers of the processes that built the planets,” says Parker. “We will use Hubble to test the theory that many planetesimals formed as binary systems from the get-go, and that today’s Kuiper Belt binaries did not come from mergers of initially solitary objects.”
Image: The SwRI-led Origins Legacy Survey will search for Kuiper Belt objects such as those shown in this artist’s illustration of a widely separated binary. Credit: Courtesy of Southwest Research Institute and Alex H. Parker.
Called the Solar System Origins Legacy Survey (SSOLS), the project represents the largest Hubble Solar System program ever, with 206 Hubble orbits around Earth allocated to it. SSOLS is conceived as a way to examine the primordial planetesimal disk with new and archival data. At stake are differing models of planetesimal formation, which predict different size and color distributions for solitary KBOs and their binary cousins.
The process of accretion would imply objects formed in isolation, later merging into binaries. In this case, the objects in binary systems would likely show dissimilar colors and a different size distribution than single KBOs. But if a process of rapid collapse was at work, producing some binary systems and some single KBOs quickly, then the expectation is for both objects in a binary system to have a similar surface color and a size distribution similar to what we find among solitary objects. At present, Hubble is the only instrument that can measure the binary occurrence rate in the Kuiper Belt, as well as the binary separation and color distribution.
SSOLS will characterize the binary and color properties of 221 KBOs, drawing on objects observed by the two largest Kuiper Belt surveys yet conducted, the Outer Solar System Origins Survey (OSSOS) and Canada-France Ecliptic Plane Survey (CFEPS). This earlier work becomes the framework within which the binary characterization of KBOs can proceed. For more, see the SSOLS website at https://www.ssols.space/, and ponder the need for the next outer system spacecraft that can take us into the realm New Horizons continues to explore.
by Paul Gilster | Apr 8, 2019 | Asteroid and Comet Deflection |
Putting a crater on an asteroid is no small matter, for it allows us to gather samples to further nail down the object’s composition. The Japan Aerospace Exploration Agency (JAXA) has achieved the feat on asteroid Ryugu using the Small Carry-on Impactor (SCI) carried by the Hayabusa2 spacecraft. Confirmation of the crater and details about its size will be forthcoming, but fortunately the spacecraft’s DCAM3 camera was able to record the event.
Following Hayabusa2 on Twitter (@haya2e_jaxa) is often the best way to keep up with operations at Ryugu (even as @OSIRISREx puts you inside that mission). The fact that we have two spacecraft in current operations around asteroids should be cause for continuing celebration. From the Hayabusa2 Twitter feed:
And with a closer look plus JAXA caption:
Image: This image captured by the camera separated from Hayabusa2 (DCAM3) shows ejection from Ryugu’s surface, which was caused by the collision of the SCI against Ryugu. Image taken at 11:36 a.m., April 5, 2019 (Indicated by the camera, Japan time). Credit: JAXA, Kobe University, Chiba Institute of Technology, The University of Occupational and Environmental Health, Kochi University, Aichi Toho University, The University of Aizu, and Tokyo University of Science.
The spacecraft protected itself before impact by moving to the other side of Ryugu to avoid any debris stirred by the collision. And while Hayabusa2 has already gathered one sample from the asteroid’s surface, the material gathered as a result of the impact should give scientists the opportunity to study what is below the surface, pristine material that dates back to the early days of the Solar System. Sample return is currently scheduled for late 2020.
As to the asteroid’s composition, the early data from Hayabusa2 have already proven useful. Says Seiji Sugita (University of Tokyo), author of a recent paper on the asteroid:
“Just a few months after we received the first data we have already made some tantalising discoveries. The primary one being the amount of water, or lack of it, Ryugu seems to possess. It’s far dryer than we expected, and given Ryugu is quite young (by asteroid standards) at around 100 million years old, this suggests its parent body was much largely devoid of water too.”
Image: Ryugu is a C-type asteroid — rich in carbon — about 900m wide. Credit: © 2019 Seiji Sugita et al., Science.
In a March 19 news conference, Sugita told an audience at the Lunar and Planetary Science Conference that Ryugu is now thought to be a fragment of one of two more distant asteroids, Eulalia or Polana. The breakup is thought to have occurred 700 million years ago. The best match in color — Ryugu is an extremely dark object — is with these two main belt asteroids, with the scientist pegging the likelihood of the relationship as high as 90 percent.
Both the visible-light camera and a near-infrared spectrometer aboard the spacecraft confirm the dearth of water, a significant result given that asteroids are thought to have supplied water to the early Earth, along with comets as well as the circumstellar disk of the system itself. Ryugu’s meager water stands in contrast to what OSIRIS-REx has found at asteroid Bennu. Although both asteroids appear similar, covered in boulders and presenting challenges to lander missions, Bennu contains considerably more water.
The paper examines a range of possibilities to explain this, but concludes that the general uniformity in color across Ryugu’s surface points to a parent asteroid that experienced internal heating caused by radioactive decay of Aluminium-26. As the authors note: “Internal heating can warm a large fraction of the volume of the parent body relatively uniformly, leaving a small volume of outer layer relatively cool.” The paper continues:
Although multiple scenarios for the evolution of Ryugu’s parent body remain viable, our comparison between Hayabusa2 remote-sensing data, meteoritic samples and asteroids leads us to prefer the scenario of parent-body partial dehydration due to internal heating. This scenario suggests that asteroids that accreted materials which condensed at ?150 K (the H2O condensation temperature under typical solar nebula conditions) must have either formed early enough to contain high concentrations of radiogenic species, such as 26Al, or formed close to the Sun where they experienced other heating mechanisms). The degree of internal heating would constrain the location and/or timing of the snow line (i.e., the dividing line between H2O condensation and evaporation) in the early Solar System.
Thus the different traits of seemingly similar asteroids like Ryugu and Bennu offer plentiful ground for studying the astrophysical processes that shaped each. The paper is Sugita et al., “The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes,” Science 19 March 2019 (abstract).
by Paul Gilster | Apr 5, 2019 | Exoplanetary Science |
An iron and nickel-rich planetesimal is apparently all that survives of a planet following the death of its star, SDSS J122859.93+104032.9. We are talking about an object in an orbit around a white dwarf so tight that it completes a revolution every two hours. Significantly, spectroscopic methods were used to make the identification, the first time a solid body has been found around a white dwarf with spectroscopy. Variations in emitted light were used to identify the gases generated by the planetesimal, with data from the Gran Telescopio Canarias in La Palma.
Lead author Christopher Manser (University of Warwick) notes the advantages of the method the team developed to study a white dwarf 400 light years away:
“Our discovery is only the second solid planetesimal found in a tight orbit around a white dwarf, with the previous one found because debris passing in front of the star blocked some of its light — that is the “transit method” widely used to discover exoplanets around Sun-like stars. To find such transits, the geometry under which we view them has to be very finely tuned, which means that each system observed for several hours mostly leads to nothing. The spectroscopic method we developed in this research can detect close-in planetesimals without the need for a specific alignment.”
Image: A planetary fragment orbits the star SDSS J122859.93+104032.9, leaving a tail of gas in its wake. Credit & copyright: University of Warwick/Mark Garlick.
This is an extreme environment, the white dwarf in question being surrounded by a debris disk through which the object passes in its orbit. The star itself is about 70 percent of the mass of the Sun and, like all white dwarfs, this one — roughly the size of Earth — is quite dense, a survivor of the star’s red giant phase. An object moving this close to the white dwarf will be under extreme gravitational stress; the gravity of SDSS J122859.93+104032.9 is fully 100,000 times that of the Earth. The fact that the team could identify a planetesimal deep within the gravitational well indicates it must be an object of great density, probably made up of iron and nickel.
On where the object came from, the paper offers this intriguing possibility:
This object may be the differentiated iron core of a larger body that has been stripped of its crust and mantle by the tidal forces of the white dwarf. The outer layers of such a body would be less dense and would disrupt at greater semimajor axes and longer periods than those required for core disruption. This disrupted material would then form a disc of dusty debris around SDSS J1228+1040, leaving a stripped corelike planetesimal orbiting within it.
Manser’s colleague and co-author Boris Gaensicke adds if the assumption that we are dealing with a planetary core is correct, then the original body would have been at least hundreds of kilometers in diameter, because it is only at this size that planets begin to differentiate, with heavier elements sinking to form a metal core. It could, of course, have been much larger.
Thus the survival of a planetesimal here, actually orbiting within the original radius of its star, suggests a large object ultimately shredded by gravitational forces. We are glimpsing what our own Solar System may resemble in 5 to 6 billion years, when it will be a white dwarf orbited by the outer planets along with asteroids and comets. Our star’s expansion into a red giant will savage the inner system, perhaps leaving debris like what we see around SDSS J122859.93+104032.9. Bear in mind, too, that the vast majority of the stars known to host planets will end their lives as white dwarfs, so we are looking at a common destiny.
The debris disk of the white dwarf is rich in magnesium, iron, silicon and oxygen, and it is within that disk that the scientists found gas streaming from the evidently solid body. The object appears to be about a kilometer in size but could be as large as a few hundred kilometers in diameter. Whether it is the source of the gas or simply the cause of the gaseous ‘tail’ as it collides with debris in the disk is not yet known. Learning more will involve studying other debris disks similar to SDSS J122859.93+104032.9 (eight gaseous white dwarf debris discs are currently known), where the spectroscopic method will perhaps find other instances of planetesimals orbiting near or within the parent star’s debris disk.
The paper is Manser et al., “A Planetesimal Orbiting Within the Debris Disc Around a White Dwarf Star,” Science April 4 2019 (abstract).
