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Using Gravitational Lensing to Reveal X-Ray Structure of a High Redshift AGN

Submitted by:
Dan Schwartz

Supermassive black holes form in the center of all massive galaxies. When the galaxies merge, the two black holes sink to the center and are thought to eventually merge, emitting gravitational radiation. Thus there should be pairs of black holes with separations on all scales. X-rays are an excellent way to identify AGN, however, no X-ray telescope exisiting or even planned can resolve two AGN separated by less than a kpc, at distance more than a 100 Mpc.

However, using gravitational lenses we can probe milli-arcsec X-ray structure and astrometry in high redshift quasars, corresponding to scales of 10-1000 pc. This project will analyze archival Chandra X-ray data of strongly lensed, quadruply imaged quasars. Many sources have 10 Chandra observations spanning more than 10 years. The student will use existing GAIA, HST or VLBI data to construct a lens mass model and formulate maximum likelihood estimates to find the best X-ray location(s) relative to the resulting radio or optical position.

Will be supported by the following grants:
AR3-24007X Chandra 16619319

Submitted on:
June 3, 2023

Characterization of the Atmospheres of Super-Earth Exoplanets with HST

Submitted by:
Mercedes Lopez-Morales

Super-earths are exoplanets smaller than Neptune, but larger than Earth. There is no such type of planets in the solar system, but they are the most common type around other stars in the Galaxy. Because of this, we are trying to understand how these planets look like, what they are made of, and if they resemble any planet in the solar system.

This project will consist of studying the atmosphere of one or more super-earths in the near IR with data from the Hubble Space Telescope. At those wavelengths, between 1.1 and 1.7 microns, the planets are expected to show water or methane features, depending on the atmospheric temperature of the planet, or no features at all if the planets are embedded in thick clouds or haze layers.

More than one-third of the over 5000 exoplanets discovered to date are super-earths, but only a handful of them have been studied in detail. Therefore, this project will contribute to our understanding of these planets.

Will be supported by the following grants:
STScI HST grants

Submitted on:
June 2, 2023

The Battle of the Energetic Particles: Galactic Cosmic Rays vs Stellar EPS at Habitable Exoplanets

Submitted by:
Federico Fraschetti

The habitability of exoplanets is an exploding field in astronomy research. Very energetic ejections of plasma (coronal mass ejections) from the star surface can strip planets of their atmospheres with dire consequences for their habitability. However, such ejections might not be very frequent on other stars due to the trapping of plasma by the very strong stellar magnetic field. As a result, the evolution of exoplanet atmospheres might instead be dominated by energetic particles (EPs) emitted by stellar flares. Thus, EPs (mostly ions) emitted by young and active stars are increasingly regarded as a major component of exoplanet atmospheric modelling and evolution.

If the planet is close to the star, the flux of stellar EPs (stEPs) is much larger than of galactic cosmic rays (GCRs), because the latter has to work against the very fast outward stellar wind. However, as the distance from the star increases, the relative flux of GCRs increases and might become comparable with the stEPs flux.

This problem has been treated so far with a variety of methods, including the Parker equation that assumes pitch-angle isotropy. However, at GeV energies this assumption might break down because the mean free path of these EPs becomes very large (a significant fraction of the stellar system size). In this project the student will solve the focused transport equation for both stEPs and GCRs in a Parker-like magnetic field and compare their fluxes for exoplanets at different distances from the host star. This will enable conclusions to be drawn regarding atmospheric ionization, evolution and survival.

Will be supported by the following grants:
TBD

Submitted on:
May 31, 2023

Studying the Nature of Galaxies Nourishing Powerful Supermassive Black Holes with Radio Jets

Submitted by:
Mojegan Azadi

Deep in the heart of every large galaxy, there is a supermassive black hole a million to a billion times more massive than our Sun. The strong gravitational force from that supermassive black hole drags the nearby gas and stars into the very center of the galaxy, releasing tremendous amounts of energy. As a result, the galaxy nucleus radiates at all wavelengths (from radio to X-rays and gamma rays). In some cases, relativistic jets emerge from the vicinity of the supermassive black holes, creating complex radio-emitting structures extending over tens of thousands of light years. These classes of active supermassive black holes are indeed among the most luminous objects in the Universe.

The impact of supermassive black holes on galaxy evolution is a longstanding unresolved issue that astronomers have been trying to address for several decades. It is not known why some galaxies trigger their central supermassive black holes to drag the nearby gas and stars actively while others do not. Neither is it known why powerful radio jets emerge from the vicinities of some supermassive black holes, but not others. To answer these questions, we will characterize the fundamental properties (such as the rate of formation of new stars and the mass of the stellar populations) of a subset of galaxies hosting supermassive black holes with the most powerful jets. This subset of galaxies, known as the 3CRR sample, lived at redshift 12, the epoch of peak cosmic star formation activity. The primary motivation of this project is to determine whether a relationship exists between supermassive black hole properties (e.g., their masses and accretion rates)and the properties of the galaxies nourishing them.

The student will be involved in several related investigations, including learning about multi-wavelength (radio, sub-millimeter, infrared, visible, UV, and X-ray) photometry, using state-of-the-art tools (spectral energy distribution modeling) used for estimating the properties of galaxies and supermassive black holes, carrying out detailed statistical analysis of the results, and participating in writing up the results into an article to be submitted to prestigious astronomical journals.

Will be supported by the following grants:
Chandra grant

Submitted on:
May 30, 2023

From Planets to Black Holes: Dips and Blips in X-ray Light Curves

Submitted by:
Rosanne Di Stefano

Short-duration events in X-ray light curves correspond to high-energy flares, gravitational lensing events, or else dips that can represent a variety of phenomena, including transits by planets. Our team discovered the first candidate planet in an external galaxy through the discovery and analysis of a short X-ray dip in a luminous X-ray source in the Whirlpool galaxy, M51. Since then, we have been developing the software and analysis tools needed to systematically search for all short-duration events observed by Chandra and other observatories. Our current work includes X-ray binaries in the Milky Way as well as external galaxies. No systematic study of short-duration X-ray phenomena in these systems has yet been conducted.

Students working with us during the 2023/2024 academic year will have the excitement of working in a forefront field, while at the same time, the advantages of more than a year of preparation that will facilitate new discoveries.

Students will have several different projects from which to choose. A student may, for example, decide to focus on flares or on dips. In either case, they may select work to identify and characterize new events, for example by machine learning or on theoretical models of the phenomena we observe or to focus on determining the physical nature(s) of the systems producing interesting events.

Students who may be interested in working on elements of this research should contact us to discuss the science and methodologies in which they would be most interested.

Will be supported by the following grants:
Smithsonian Scholarly Studies Program

Submitted on:
May 29, 2023

AI-Assisted X-Ray Source Classification and Discovery of Extreme X-Ray Sources

Submitted by:
Dong-Woo Kim

Multi-wavelength studies of X-ray sources allow for discovering unexpected and paradigm-changing sources, such as X-ray bright optically normal galaxies (XBONGS), which are supermassive black holes hidden behind massive layers of dust (see press release1). Compared with the previous version, the improved Chandra Source Catalog (v2.1) will have 25% more X-ray sources with more accurate source positions. In this project, the student will explore the new Chandra X-ray sources cross-matched with optical/IR/UV/radio surveys using tools of machine learning to accomplish the following goals:

  • Improve the separation between different types of objects (stars, galaxies, XBONGs, AGNs, and QSOs) in the multi-wavelength parameter space of properties. This will be achieved using unsupervised and supervised machine learning techniques and will improve on current methods that rely on linear separations.
  • Find the most extreme relationships among multi-wavelength properties that will unveil new types of objects, such as XBONGs, by systematically applying an anomaly detection algorithm to the cross-matched catalog. Methods include unsupervised random forest and dimensionality reduction.
  • The student will get acquainted with AI software tools, the physics of extreme accretion events in the universe, as well as data science techniques for exploring large datasets. Knowledge of Python programming is preferred, but previous experience in astronomy and astrophysics is not required. The ASTRO-AI team2 at the Center for Astrophysics Harvard and Smithsonian will support this project, when necessary, e.g., in applying the essential s/w tools and interpreting the outputs.

Additional information:

https://chandra.harvard.edu/photo/2023/xbongs/index.html

https://astroai.cfa.harvard.edu

Will be supported by the following grants:
Chandra grant

Submitted on:
May 28, 2023

Machine Learning Investigations of Black-Hole X-ray Binaries

Submitted by:
Jack Steiner

NICER is the premier soft X-ray timing instrument on the X-ray sky, and operates from the International Space Station. NICER is amassing an unprecedented archive of X-ray spectral-timing data on the brightest objects in the X-ray sky -blackholeX-ray binaries. Several of these objects are persistent, but the vast majority undergo year-long outbursts which are marked by transitions through a pattern of spectral-timing states. During these outbursts, blackholes launch relativistic jets, emit powerful winds, and produce dynamic humming patterns known as quasi-periodic oscillations (QPOs).

NICER has produced tens of thousands of observations of these systems, often consisting of near-daily snapshots during an outburst. For the interested student, we will be applying (python-based) machine-learning / AI algorithms to explore the properties of these rich X-ray binary systems. Candidate topics include investigations of outflowing winds, determining black-hole spins and inclinations, spectral and QPO cross-connections, or classification algorithms to automatically determine spectral state or distinguish between black-hole and neutron-star systems. We will discuss these and other options to hone in on a specific project based on the students particular interests.

Will be supported by the following grants:
NICER / NuSTAR observing grants

Submitted on:
May 24, 2023

How Magnetic Fields Guide Star-forming Flows

Submitted by:
Phil Myers

Star formation is the primary baryonic process driving the evolution of the Universe. Despite its central importance to astrophysics, cosmology, and life in the Universe, star formation is still poorly understood. Magnetic fields are thought to play a crucial role in the puzzle. Strong fields can prevent gravitational collapse and star formation, while moderate fields can affect the masses and numbers of stars a cloud will form. We have recently obtained unprecedented high quality polarization maps of star-forming regions and now have a good chance to solve the star formation puzzle. The maps were made at far infrared wavelengths with NASAs Stratospheric Observatory for Infrared Astronomy (SOFIA) - a remarkable 2.7m infrared telescope flown on a specially modified Boeing 747 airplane.

The student will analyze these new SOFIA polarization maps of molecular clouds, from immense filaments forming massive star clusters, down to small dense cores forming just a few stars like our Sun. The magnetic maps will be combined with observations of molecular spectral lines. They will tell us how magnetic fields prevent collapse in different gas clouds, whether inflowing gas is dominated by chaotic, turbulent flows or is regulated and inhibited by magnetic fields. They will indicate the conditions where inflowing and ejected gas is channeled along field lines. The research should provide exciting new results on star formation.

The research will be guided by Myers, Stephens, and other team members. The student will be encouraged to lead publication of in a professional astrophysics journal. A recent Southampton student did very well with a similar project.

Recent SOFIA Observing Programs with P. Myers as co-I:
FIELDMAPS - cycle 8 magnetic studies of large cluster-forming filaments in the Milky Way (PI Stephens)
SIMPLIFI - cycle 9 magnetic studies of local star-forming filaments with finer resolution (PI Pillai)

Recent Papers:
Myers et al. 2018, ApJ, 868, 51 Myers et al. 2020, ApJ, 896, 163 Myers Basu 2021, ApJ 917,35 Pillai et al. 2020, NatAs 4, 1195, Stephens et al. 2022, ApJ, 926L, 6.

Project Advisors: Philip Myers (CfA) Ian Stephens (Worcester State University), Thushara Pillai (Haystack Observatory)

Additional information:
https://www.sofia.usra.edu/observing-programs/legacy-programs

Will be supported by the following grants:
Student AAS travel will be supported by SOFIA grants to proposal ID 08_0186 (FIELDMAPS) and 09_0215 (SIMPLIFI)

Submitted on:
May 24, 2023

What Suppresses Star Formation at the Center of the Galaxy?

Submitted by:
Qizhou Zhang

The central molecular zone (CMZ), the inner 500 pc of the Milky Way, harbors the most extreme physical conditions for star formation in the Galaxy. The gas properties, radiation field, and cosmic ray ionization rate are more similar to those in the center of other galaxies, starbursts and high redshift galaxies than in the Solar neighborhood clouds. Thanks to its proximity, CMZ is the only extreme environment in which individual forming stars can be spatially resolved and allows linking the small-scale physics of star formation and feedback with the galactic-scale processes that together drive the evolution of galaxies.

Despite the large reservoir of dense molecular gas in the CMZ that rivals starburst regions in external galaxies, its average star formation efficiency is more than a factor of 10 lower than in the Milky Way disk and starburst galaxies. What is the underlying cause of such a low rate of star formation? Strong turbulence and Galactic shear may raise the density threshold and suppress star formation in the CMZ. Magnetic fields can also suppress star formation. In this project , we will explore the full polarization data from SOFIA that probes magnetic fields in the CMZ. In conjunction with the ALMA large program ACES (The ALMA CMZ Exploration Survey), we will explore the effect of magnetic fields on the gas dynamics, fragmentation of clouds, and formation of dense cores in protoclusters.

The student will have the opportunity to analyze the magnetic field data to estimate the field strength, and cross correlate magnetic field properties with signs of star formation revealed by ALMA. This will be the first systematic assessment of magnetic fields in the CMZ. The student is encouraged to lead a publication reporting findings from the project in an astrophysical journal.

Additional information:
https://lweb.cfa.harvard.edu/~qzhang/

Will be supported by the following grants:
NSF

Submitted on:
May 23, 2023