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Hubble Captures Star Formation in Motion: Inside Lupus 3 and NGC 1333


Hubble Captures Star Formation in Motion: Inside Lupus 3 and NGC 1333

Star formation begins inside cold molecular clouds, where gravity slowly overwhelms thermal pressure and turbulence. These environments remain difficult to study because dust absorbs visible light and hides the earliest stages of stellar evolution. Space-based telescopes with high spatial resolution and multiwavelength capability, therefore, play a critical role in understanding how stars form and evolve. The Hubble Space Telescope continues to make a decisive contribution in this area.

Two recent Hubble observations focus on nearby star-forming regions within the Milky Way. One image targets the Lupus 3 molecular cloud. The other examines NGC 1333 in the Perseus molecular complex. Although these regions differ in structure and density, both reveal active stellar nurseries. Together, they provide a detailed view of early stellar evolution across multiple stages. These observations resolve circumstellar disks, trace stellar variability, and show how newly formed stars interact with their environment. As a result, they strengthen current models of star formation and help connect theory with observation.

Lupus 3: A nearby laboratory for low-mass star formation

Lupus 3 lies approximately 500 light-years from Earth in the constellation Scorpius. It forms part of the larger Lupus molecular cloud complex. Compared to massive star-forming regions, Lupus 3 appears relatively sparse. However, this apparent simplicity makes it an ideal target for studying low-mass star formation.

Hubble’s image reveals a diffuse cloud threaded with dark dust lanes. Embedded within this structure are numerous young stars. Most belong to the T Tauri class. These stars have already emerged from their natal envelopes but have not yet reached the main sequence. Their ages typically remain below ten million years.

T Tauri stars continue to contract under gravity. At the same time, they accrete material from surrounding disks. This accretion process drives variability in both brightness and spectral output. Hubble resolves these stars individually, allowing astronomers to study them in context rather than isolation.

Meanwhile, illuminated gas highlights regions where stellar radiation interacts with the cloud. In contrast, opaque dust marks areas of higher density. These dense pockets may collapse in the future, extending star formation within Lupus 3. The image, therefore, captures both current activity and potential future evolution.

A seemingly serene landscape of gas and dust is hopping with star formation behind the scenes in the Lupus 3 region. Credit: NASA, ESA, and K. Stapelfeldt (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)
A seemingly serene landscape of gas and dust is hopping with star formation behind the scenes in the Lupus 3 region. Credit: NASA, ESA, and K. Stapelfeldt (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)

Photometric variability and the nature of stellar youth

The Lupus 3 observation places particular emphasis on stellar variability. Many of the T Tauri stars in the region show irregular changes in brightness. These variations arise from multiple physical processes acting simultaneously.

First, rotating starspots modulate visible light output. Second, episodic accretion events deposit energy onto the stellar surface. Third, circumstellar material intermittently obscures the star. Each mechanism leaves a distinct observational signature.

Hubble’s stability allows astronomers to measure these effects precisely. Over time, such data improve constraints on stellar rotation rates and magnetic field strength. They also clarify how mass transfer from disk to star proceeds during early evolution.

Importantly, these processes influence disk survival. Strong magnetic activity and stellar winds can erode circumstellar material. As a result, they affect the window of opportunity for planet formation. Lupus 3 provides insight into how young stars shape their own planetary environments.

Close-up (cropped view) of a dark dust cloud in the Lupus 3 region. Credit: NASA, ESA, and K. Stapelfeldt (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)
Close-up (cropped view) of a dark dust cloud in the Lupus 3 region. Credit: NASA, ESA, and K. Stapelfeldt (Jet Propulsion Laboratory); Processing: Gladys Kober (NASA/Catholic University of America)

NGC 1333: Multiple phases of stellar birth

NGC 1333 lies deeper within the Perseus molecular cloud at a distance of roughly 950 light-years. Unlike Lupus 3, this region contains a dense concentration of young stellar objects. Hubble’s image reflects that complexity. Within a single field of view, the observation captures protostars, pre-main-sequence stars, and variable young objects. The most striking feature is a deeply embedded protostar surrounded by a thick circumstellar disk.

This disk blocks direct starlight and casts pronounced shadows into the surrounding nebula. These shadows confirm the disk’s geometry and orientation. They also indicate a substantial mass reservoir feeding the growing star.

At the same time, outflows emerge from the protostar’s poles. These jets clear cavities in the surrounding cloud. Light escapes along these channels and scatters off dust grains. The result is a structured reflection nebula shaped by stellar feedback. This interaction between inflow and outflow defines the protostellar phase. NGC 1333 provides a direct observational window into one of the most critical stages of star formation.

A bright reflection nebula shares the stage with a protostar and planet-forming disk in this Hubble image of NGC 1333. Credit: NASA, ESA, K. Stapelfeldt (Jet Propulsion Laboratory) and D. Watson (University of Rochester); Processing: Gladys Kober (NASA/Catholic University of America)
A bright reflection nebula shares the stage with a protostar and planet-forming disk in this Hubble image of NGC 1333. Credit: NASA, ESA, K. Stapelfeldt (Jet Propulsion Laboratory) and D. Watson (University of Rochester); Processing: Gladys Kober (NASA/Catholic University of America)

Disks and jets: The regulators of stellar growth

Circumstellar disks play a central role in early stellar evolution. They regulate angular momentum and control accretion. Without them, stars could not form efficiently. The NGC 1333 image highlights these disks through both direct and indirect signatures.

Disk shadows offer one of the clearest indicators. They require a disk thick enough to block light and extended enough to influence the surrounding cloud. Observing these features helps constrain disk mass and vertical structure.

Jets and outflows provide the counterbalance. They remove excess angular momentum and limit stellar mass growth. They also inject energy into the cloud, altering local conditions. In some cases, this feedback may trigger additional star formation nearby.

Hubble’s resolution allows astronomers to disentangle these competing effects. By observing multiple objects within NGC 1333, researchers compare how similar processes unfold under slightly different conditions.

The two stars, HBC 340 (lower) and HBC 341 (upper), unleash stellar winds, or material flowing from the surface of the star, that clear out the cavity from the surrounding molecular cloud over time. Credit: NASA, ESA, K. Stapelfeldt (Jet Propulsion Laboratory) and D. Watson (University of Rochester); Processing: Gladys Kober (NASA/Catholic University of America)
The two stars, HBC 340 (lower) and HBC 341 (upper), unleash stellar winds, or material flowing from the surface of the star, that clear out the cavity from the surrounding molecular cloud over time. Credit: NASA, ESA, K. Stapelfeldt (Jet Propulsion Laboratory) and D. Watson (University of Rochester); Processing: Gladys Kober (NASA/Catholic University of America)

Multiwavelength imaging and the role of dust

Dust governs much of what Hubble observes in these regions. While dust obscures visible light, it also reflects and scatters it. This dual role shapes the appearance of both Lupus 3 and NGC 1333. Hubble combines visible and near-infrared data to overcome these limitations. Near-infrared light penetrates deeper into dusty regions. Visible light traces reflection, nebulosity, and ionized gas. Together, these wavelengths reveal a layered structure.

In Lupus 3, this approach highlights diffuse clouds and exposed young stars. In NGC 1333, it reveals embedded protostars and disk shadows. The same technique thus adapts to different environments.

Observations of nearby stellar nurseries test theoretical models. Simulations predict how clouds fragment, how disks evolve, and how feedback shapes environments. Hubble’s images offer real benchmarks against which these predictions must align. Lupus 3 supports models of low-mass star formation in relatively calm environments. NGC 1333, in contrast, illustrates clustered formation with strong feedback. Together, they show the diversity of star-forming conditions within the same galaxy.

An actively forming star called a protostar casts its glow on the surrounding gas and dust. Credit: NASA, ESA, K. Stapelfeldt (Jet Propulsion Laboratory) and D. Watson (University of Rochester); Processing: Gladys Kober (NASA/Catholic University of America)
An actively forming star called a protostar casts its glow on the surrounding gas and dust. Credit: NASA, ESA, K. Stapelfeldt (Jet Propulsion Laboratory) and D. Watson (University of Rochester); Processing: Gladys Kober (NASA/Catholic University of America)

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