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A large misalignment between continuous jet and discrete ejecta in microquasar GRS 1915+105 during its obscured phase

Using the East Asian VLBI network, researchers discovered a significant and recurrent misalignment between the continuous jet and discrete ejecta in the microquasar GRS 1915+105 during its obscured phase, suggesting a warped accretion disk alters the jet launching geometry.

Original authors: Wu Jiang, Xi Yan, Zhen Yan, Ya-Ping Li, Lang Cui, Zhi-Qiang Shen

Published 2026-04-02

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CC BY 4.0

Original authors: Wu Jiang, Xi Yan, Zhen Yan, Ya-Ping Li, Lang Cui, Zhi-Qiang Shen

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Cosmic "Whiplash": A Black Hole's Jet Goes Off-Script

Imagine a lighthouse in the middle of a stormy ocean. For decades, this lighthouse has been spinning its beam in a perfectly steady, predictable circle. That's GRS 1915+105, a famous black hole system in our galaxy. It's known as a "microquasar" because it acts like a tiny version of a massive galaxy, shooting out powerful beams of energy (jets) from its poles.

For 30 years, astronomers have watched this lighthouse. They knew exactly where the beam pointed: a steady direction toward the Southeast and Northwest. They also knew that occasionally, the black hole would spit out huge, fast-moving "bullets" of gas (discrete ejecta) that zoomed away at nearly the speed of light.

But in 2023, something weird happened.

The Plot Twist

In April and again in September 2023, the black hole went through a "dark phase." It got covered up by a thick cloud of dust and gas, hiding its X-ray light from us. But while it was hiding, the East Asian VLBI Network (a giant telescope made by linking radio dishes across Asia) caught it in the act.

They saw two things happening at the same time, but they were pointing in completely different directions:

The Steady Stream (Continuous Jet): The core of the black hole was still shooting out a steady, continuous stream of energy. This stream was pointing in the old, familiar direction (Southeast/Northwest). It was like the lighthouse beam that never changes.
The Wild Bullets (Discrete Ejecta): Suddenly, the black hole shot out new "bullets" of gas. But instead of following the lighthouse beam, these bullets shot out in a totally different direction (almost North/South).

The Analogy: Imagine a sprinkler system in a garden. The main hose (the continuous jet) is fixed to the ground and sprays water in a steady arc. Suddenly, someone kicks the nozzle, and a massive burst of water shoots out sideways, hitting a completely different part of the lawn. That's what happened here. The "bullets" were misaligned by about 40 degrees—a huge angle in space—and they were moving much slower than usual.

Why Did This Happen? The "Tilted Disk" Theory

The authors of the paper propose a dramatic explanation: The black hole's dinner plate got warped.

Black holes eat gas from a spinning disk around them (the accretion disk). Usually, this disk is flat, like a pizza. The black hole's spin and the disk are aligned, so the jets shoot straight up and down.

But the researchers think something massive and invisible (like a passing star or a third object in the system) flew too close to the black hole. This "flyby" acted like a giant hand grabbing the edge of the pizza and twisting it.

The Outer Edge: The outer part of the disk got twisted and warped. When the black hole shot out the "bullets" (discrete ejecta) from this twisted section, they flew off in the new, tilted direction.
The Inner Core: The part of the disk closest to the black hole is heavy and stubborn. It quickly snapped back into alignment with the black hole's own spin. So, the steady stream (continuous jet) kept pointing in the original, correct direction.

This explains why the two jets were pointing in different directions at the same time. It also explains why the system got "obscured" (hidden): the twisted outer disk tilted up and blocked our view of the bright center, like a person leaning over a table and blocking a candle.

The "Flyby" Evidence

The paper suggests this wasn't just a random glitch. The suddenness of the change implies an external force. The authors ran computer simulations showing that if a heavy object (like a rogue star) flies past the system, it can tear the outer disk apart and warp it, exactly matching what they saw.

Why Does This Matter?

This discovery is a big deal for two reasons:

It solves a mystery: Scientists have debated for years whether the steady jets and the explosive "bullets" come from the same place or different mechanisms. This paper suggests they come from different parts of the disk: the steady jet comes from the stable inner core, while the wild bullets come from the chaotic, warped outer edges.
It helps us understand the universe: This "obscured phase" where a black hole gets hidden by its own twisted disk might happen in other systems, including supermassive black holes in the centers of other galaxies. Understanding this helps us figure out why some galaxies suddenly change their appearance.

In short: The black hole GRS 1915+105 got a cosmic "whiplash" from a passing object. Its outer disk got twisted, sending new jets flying off in a new direction, while its inner core stayed calm and kept pointing the old way. It's a cosmic dance where the music changed, but the dancers didn't quite get the memo at the same time.

1. Problem Statement

The microquasar GRS 1915+105, a Galactic low-mass X-ray binary (LMXB), has been extensively studied for over three decades. Historically, its relativistic jets (both continuous and discrete) have been observed to maintain a stable Position Angle (PA) of approximately $147^\circ$ (SE–NW direction) and a Viewing Angle (VA) of $\sim 64^\circ$ . However, since 2019, the source has entered an "obscured phase" characterized by heavy X-ray absorption ( $N_H > 10^{23} \text{--} 10^{24} \text{ cm}^{-2}$ ) while remaining active in radio and infrared bands. The physical mechanism driving this obscuration and its potential impact on jet launching geometry remained unclear. Specifically, it was unknown whether the continuous jet (associated with the inner accretion flow) and discrete ejecta (transient jets) share a common launching axis or if their geometries decouple during such obscured states.

2. Methodology

The authors conducted a multi-epoch, multi-frequency Very Long Baseline Interferometry (VLBI) campaign using the East Asian VLBI Network (EAVN) and archival data from the Karl G. Jansky Very Large Array (VLA).

Observations:
- EAVN: Observed GRS 1915+105 during a radio flare in April 2023 at two frequencies: 6.7 GHz (tracing discrete ejecta) and 43 GHz (tracing the compact continuous jet core). Six epochs were observed.
- VLA: Analyzed archival X-band (10 GHz) data from September 2023 to study a subsequent flare event.
Data Reduction:
- EAVN data were calibrated using AIPS and self-calibrated in DIFMAP. Phase referencing was employed using calibrator J1925+1227 to ensure astrometric precision.
- VLA data were processed using the CASA pipeline.
Analysis Techniques:
- Model Fitting: The source structure was modeled using circular and elliptical Gaussian functions (via DIFMAP's MODELFIT) to extract flux density, radial distance, size, and PA for the core and ejecta components.
- Kinematics: Apparent speeds were derived via linear fitting of component positions over time. Intrinsic velocities and Viewing Angles were calculated using standard relativistic kinematic equations.
- Simulations: To explain the sudden geometric changes, the authors performed Smoothed Particle Hydrodynamics (SPH) simulations using the PHANTOM code. They modeled a thin accretion disk perturbed by a flyby object (mass $3 M_\odot$ , pericenter 0.5 AU) on a parabolic orbit to test if tidal forces could induce disk warping.

3. Key Contributions

First Direct Observation of Decoupled Jet Axes: The study provides the first simultaneous, high-resolution resolution of a continuous jet and discrete ejecta in GRS 1915+105 showing a massive angular misalignment.
Characterization of the "Obscured Phase" Jet Physics: It links the X-ray obscured state directly to a time-variable jet launching geometry, challenging the assumption of a single, fixed jet axis.
Mechanism Proposal: The authors propose a unified scenario where an external perturbation (flyby/tertiary object) warps the outer accretion disk, causing discrete ejecta to launch from tilted sub-disks, while the inner disk rapidly realigns with the black hole spin, maintaining the stable continuous jet.
Simulation Validation: The paper provides numerical evidence that a single flyby event can generate the necessary disk warping ( $\sim 20^\circ$ in simulation, potentially higher with non-linear coupling) to explain the observed $\sim 40^\circ$ misalignment.

4. Key Results

A. Large Misalignment of Position Angles

Continuous Jet (43 GHz): The inner continuous jet maintained a PA of $146^\circ \text{--} 158^\circ$ , consistent with the historical long-standing jet direction ( $\sim 147^\circ$ ).
Discrete Ejecta (6.7 GHz & 10 GHz): The discrete ejecta launched during the April 2023 and September 2023 flares exhibited a PA of $\sim 188^\circ$ (April) and $\sim 174^\circ$ (September).
Angular Deviation: The misalignment between the continuous jet and discrete ejecta reached $\sim 40^\circ \text{--} 46^\circ$ , a significant departure from the stable SE–NW axis observed for decades.

B. Low Intrinsic Velocity

The discrete ejecta in April 2023 moved with apparent speeds of $\sim 6.5 \text{ mas day}^{-1}$ .
Given the new Viewing Angle of $89^\circ \pm 1^\circ$ (nearly edge-on), the intrinsic velocity was calculated to be $\sim 0.35 c$ .
This is the slowest intrinsic velocity ever reported for GRS 1915+105, contrasting sharply with previous relativistic jets ( $> 0.9 c$ ) observed when the system was not obscured.

C. Recurrence

A similar misalignment was detected in a subsequent flare in September 2023, confirming that the time-variable jet geometry is a recurrent feature of the obscured phase, not a one-off anomaly.

D. Simulation Results

The SPH simulation of a flyby object induced a warp in the outer disk with an amplitude of $\sim 20^\circ$ . The authors argue that non-linear coupling between the warped disk and transient jets could amplify this to the observed $\sim 46^\circ$ .
The simulation supports the hypothesis that the outer disk is torn or tilted, while the inner disk remains aligned with the black hole spin (Bardeen-Petterson effect), explaining the coexistence of two distinct jet directions.

5. Significance

Jet Launching Mechanisms: The results support the hypothesis that continuous jets and transient discrete ejecta in Black Hole X-Ray Binaries (BHXRBs) may originate from fundamentally different regions or mechanisms. The continuous jet appears tied to the stable black hole spin axis, while discrete ejecta can be launched from the dynamically evolving, warped outer accretion disk.
Understanding Obscured Phases: The study offers a physical explanation for the "obscured phase" in GRS 1915+105 and analogous systems (like V404 Cyg) and X-ray Changing-Look Active Galactic Nuclei (CLAGN). It suggests that X-ray obscuration is caused by a warped or thickened outer disk moving into the line of sight, rather than just a change in accretion rate.
External Perturbations: The detection of such a dramatic, sudden change after 30 years of stability implies the action of an external torque, likely a close flyby of a tertiary object or a massive companion, providing a new diagnostic tool for detecting unseen companions in binary systems via astrometric deviations.
General Astrophysical Implications: The findings provide a crucial clue for understanding transient phenomena in accreting systems, suggesting that disk warping and tearing are key drivers of jet reorientation and X-ray obscuration across different mass scales (from stellar-mass black holes to supermassive black holes).