TSST

A time-domain astronomy collaboration

Transient science @
space telescope.

From exploding stars to feeding black holes, we use the world’s most powerful observatories to catch the cosmos in the act of changing.

Explore our science ↘ Meet the transient hunters
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About TSST

A universe that
refuses to stand still.

Transient Science @ Space Telescope brings together observers, theorists, and data scientists to understand the brief, brilliant events that reshape our universe.

We are a compact team within the Space Telescope Science Institute and Johns Hopkins University. We meet weekly, pool resources and expertise, and collaborate across rapid-response observations, archival discovery, precision cosmology, and new computational tools.

Science Blocks

Four questions.
One changing universe.

Our four Science Blocks organize the team’s core research. Select a block title to explore its questions, methods, and connected projects.

Diagram of a supernova interacting with a dusty circumstellar environment

Tracing dust formation, shock breakout, circumstellar interaction, and the final evolutionary stages of massive stars from the ultraviolet through the infrared.

Block LeadMelissa Shahbandeh

Deputy LeadName to be added

Hubble survey footprint over a deep extragalactic field

Finding and characterizing distant supernovae to study how stellar explosions, their environments, and the expansion of the universe evolve across cosmic time.

Block LeadDave Coulter

Deputy LeadName to be added

Strongly lensed galaxy field with multiple supernova images marked

Using multiply imaged supernovae and their time delays to test cosmology, dark energy, and the expansion rate of the universe.

Block LeadJustin Pierel

Deputy LeadName to be added

K2 Supernova Cosmology Experiment mission emblem

Improving Type Ia supernova observations, models, and systematics to sharpen constraints on dark energy and the history of cosmic expansion.

Block LeadMike Engesser

Deputy LeadName to be added

Beyond the Blocks

Ideas that cross
the boundaries.

Focused observing programs, discovery efforts, and tools that connect multiple areas of the team’s science.

Hubble survey footprints across a deep star field with a peanut graphic

Our “NUTS” HST program explores the fast ultraviolet sky, using early shock breakout and shock-cooling light to constrain core-collapse supernova progenitors.

Artist’s impression of an extreme stellar explosion

All-sky surveys reveal tidal disruption events, superluminous and pair-instability supernova candidates, and rare explosions that challenge existing classifications.

Colorful expanding supernova remnant surrounding a central star

A systematic search for surviving companions to stripped-envelope supernovae tests binary evolution, companion fractions, and stellar-mass distributions.

K2 Supernova Cosmology Experiment mission emblem

High-cadence space-based light curves expose the earliest phases of supernovae and other explosions that conventional ground surveys often miss.

Profile illustration combining a human face with a neural network

Classification tools such as FLEET help prioritize the most scientifically valuable events within the accelerating stream of survey discoveries.

Dust + Core-Collapse Explosions

We connect the earliest moments of core collapse to the dusty environments that record a massive star’s final years.

What we investigate

Ultraviolet shock breakout constrains progenitor radii and explosion energetics, while infrared emission reveals whether dust formed in the ejecta or was already present in the circumstellar medium.

Our JWST programs study mid-infrared emission beyond the standard radioactive supernova light curve. By separating newly formed ejecta dust from pre-existing circumstellar dust, the observations probe late-stage massive-star evolution and the contribution of supernovae to the Universe’s dust budget.

Projects within this block

  • Narrow-Field NUV Transient Survey (NUTS)
  • Dusty SNe with JWST — GO programs 1860 and 2666
  • Long Lost Companions
  • Core-collapse events observed by Kepler and TESS

High-z SNe

Distant supernovae let us study stellar death and cosmic expansion when the universe was much younger.

What we investigate

Deep Hubble, Webb, and future Roman observations extend transient discovery to higher redshift, where cadence, selection effects, host-galaxy environments, and reliable classification become central challenges.

Work within this block

  • Deep-field transient searches
  • High-redshift discovery and classification
  • Survey selection-function studies
  • Preparation for Roman time-domain observations

Lensed SNe

A single explosion seen along several paths through curved spacetime becomes a precise cosmological clock.

What we investigate

Time delays between multiple images constrain the expansion rate of the universe. Predictable supernova light curves can yield precise delays on shorter timescales than variable quasars.

Work within this block

  • Improved supernova time-delay measurements
  • Roman discovery and cosmology forecasts
  • Rapid Hubble follow-up of ground-based discoveries
  • Lens and microlensing systematics

SN Ia Cosmology

Type Ia supernovae map the expansion history of the universe—but realizing their full precision requires understanding the explosions themselves.

What we investigate

Early light curves, progenitor environments, calibration, population evolution, and other systematic effects connect supernova physics to robust measurements of dark energy.

Work within this block

  • Early-time Kepler and TESS light curves
  • Type Ia progenitor constraints
  • Distance-measurement systematics
  • Dark-energy and expansion-history analyses

Narrow-Field NUV Transient Survey

NUTS explores one of time-domain astronomy’s next frontiers: the rapidly changing ultraviolet sky.

The science

Very early ultraviolet peaks from shock breakout and shock cooling encode the progenitor star’s radius and the explosion energy per unit ejecta mass.

The program

The HST GOODS-S survey pairs deep near-ultraviolet imaging with a fast cadence and coordinated ground-based observations to locate and time supernova discoveries.

Extreme Transients

Wide-field surveys are uncovering rare explosions and flares that stretch—and sometimes escape—established classifications.

Targets

The team studies tidal disruption events, superluminous supernovae, pair-instability candidates, and unexpected classes of rapidly changing phenomena.

Why they matter

These events probe black-hole feeding, the deaths of the most massive stars, and physical regimes that ordinary supernova samples cannot reach.

Long Lost Companions

Surviving companion stars can reveal whether stripped-envelope supernovae arise predominantly from single stars or interacting binaries.

The science

Direct companion searches test binary evolution and constrain the companion fraction, stellar types, and mass distribution of supernova progenitor systems.

The approach

Rather than relying on isolated examples, the program builds a statistically meaningful Hubble sample across SNe IIb, Ib, and Ic.

Transients with Kepler & TESS

Continuous, high-precision light curves open a view of the first hours of an explosion that ground-based surveys rarely capture.

What we measure

Early features constrain Type Ia companions, explosion physics, core-collapse progenitor radii, and shock breakout.

Broader reach

The same data reveal rare superluminous supernovae, tidal disruption events, kilonovae, and other fast transients.

Machine Learning for Transients

Modern surveys discover far more transients than can be classified spectroscopically, making intelligent prioritization essential.

FLEET

Finding Luminous and Exotic Extragalactic Transients assigns discovery probabilities so limited follow-up time can target the most valuable candidates.

Looking ahead

Expanding these methods to more transient classes prepares the team for the much larger discovery streams expected from next-generation surveys.

The people

STScI’s
Transients.

A collaborative group of scientists based at STScI, Johns Hopkins University, and partner institutions.

We share expertise across supernovae, tidal disruption events, cosmology, gravitational lensing, dust, light echoes, machine learning, and software development.

Ori Fox
Full Scientist · STScI

Ori Fox

Supernovae · Progenitors · Dust · CSM interaction

Armin Rest
Full Astronomer · STScI / JHU

Armin Rest

Supernovae · Light echoes · Cosmology · Big data

Louis-Gregory Strolger
Observatory Scientist / Research Scientist · STScI / JHU

Louis-Gregory Strolger

Star formation · Supernovae · Stellar evolution

From NASA ADS

Research with
lasting impact.

Each team member’s three most-cited first-author refereed papers, synchronized weekly from the Astrophysics Data System.

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Citation counts change over time and are supplied by NASA ADS ↗.

Stay curious

Something extraordinary
could happen tonight.

Connect with us as we explore the changing sky with Hubble, Webb, Roman, and the next generation of time-domain surveys.

Work with us

Collaborate

Have a transient, observing program, dataset, or research idea that overlaps with our work? We welcome conversations across institutions and disciplines.

Start a conversation

Meet the team

Visit a Meeting

Researchers, students, and visitors can request an invitation to join a TSST meeting or share recent transient-science work with the team.

Request an invitation