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The Changing Brightness of Quasars

Quasars vary in brightness due to black hole mass and accretion disc dynamics.

C. Wolf, S. Lai, J. -J. Tang, J. Tonry

― 5 min read

Quasar Brightness Quasar Brightness Explained brightness changes. Investigating the reasons behind quasar
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Quasars are very bright objects in the universe, powered by supermassive Black Holes at the centers of galaxies. They shine so brightly because they pull in gas and dust, creating a swirling disc of material around them. This disc gets hot and emits Light, making quasars some of the most luminous objects in the universe.

What Causes Quasar Brightness Changes?

One of the interesting things about quasars is that their brightness doesn't stay the same. Instead, they can change brightness over time, sometimes dramatically. Scientists are keen to figure out why this happens and how it relates to the black holes themselves.

The variation in brightness appears to depend on several factors. One of the significant factors is the Mass of the black hole at the center of the quasar. It seems that the bigger the black hole, the more complex the light variations can get. This happens because a more massive black hole has a larger event horizon, which is the point beyond which nothing can escape its pull, influencing how material falls into it.

The Role of Time

Another important aspect is time. Different wavelengths of light can vary at different rates. For example, ultraviolet light, which has a shorter wavelength than optical light, might change in brightness quicker than optical light. This time variation gives clues about the processes happening in the accretion disc, the disc of material swirling around the black hole.

The Accretion Disc Explained

So, what exactly is this accretion disc? Picture it like a merry-go-round at a funfair. The material falls into the black hole and starts spinning around it, much like kids riding the carousel. As they spin around faster, they feel the pull of the center stronger, which heats up the material and creates the brilliant light we see from Earth.

The closer the material is to the black hole, the hotter it gets. This hot material emits light across the spectrum-from radio waves to gamma rays. The brighter the quasar, the more energy it’s pumping out, and the more we can learn about it.

Observing Quasars

To study these changes in brightness and understand what’s going on inside these quasars, astronomers use a variety of tools, including telescopes that can observe in different wavelengths.

Over the years, much data has been collected, allowing scientists to build a picture of quasar behavior. They watch how brightness changes over days, months, or even years, looking for patterns. By analyzing these patterns, they can gain insights into the physics of these distant objects.

Analyzing Brightness Changes

When scientists look at the brightness changes, they often use something called a structure function, which can be thought of like a scorecard for how much brightness changes over time.

Imagine trying to summarize a basketball game with just one number for the score-it wouldn't tell you much about the game. A structure function provides a richer understanding by taking multiple snapshots of brightness changes over different time scales. By doing this, scientists can determine how much variability there is in the brightness of quasars and at what time scales these changes occur.

What Do These Changes Mean?

These brightness changes can help scientists learn about a quasar's black hole. For instance, they can estimate the mass of the black hole by looking at how quickly the light changes. It’s like guessing the weight of a cake by how it wiggles on the plate.

Additionally, these changes in brightness can hint at the conditions in the accretion disc. For example, if the brightness changes a lot, it might suggest that material is falling in more rapidly or that there are other complex interactions happening in the disc.

The Importance of Black Hole Mass

The mass of the black hole plays an essential role in determining the behavior of the accretion disc and, thus, the brightness variations. For smaller black holes, the variations seem to be more straightforward. However, as black holes become more massive, the relationship becomes more complex, with varying brightness over a wider range of time scales.

This complexity is somewhat expected. It’s like having a small candle flickering in the wind versus a giant bonfire-small changes in conditions affect them quite differently.

Looking Ahead

As technology improves, astronomers expect to collect even more data on quasars. Upcoming surveys will allow scientists to study these objects in much greater detail. They might even uncover new behaviors or patterns that have yet to be seen.

By analyzing the light from quasars, scientists can learn more about how galaxies grow and evolve. Quasars serve as light houses, guiding researchers on their quest to understand the universe.

Conclusion

Quasars are fascinating cosmic objects fueled by black holes. Their brightness changes, driven by the complex dynamics of Accretion Discs, provide valuable insights into the nature of black holes and their growth. With ongoing research and advancements in technology, we are sure to learn even more about these remarkable objects in the universe.

Who knew that studying distant snacks for black holes could be so enlightening?

Original Source

Title: Timescales of Quasar Accretion Discs from Low to High Black Hole Masses and new Variability Structure Functions at the High Masses

Abstract: The UV-optical variability of quasars appears to depend on black-hole mass $M_{\rm BH}$ through physical timescales in the accretion disc. Here, we calculate mean emission radii, $R_{\rm mean}$, and orbital timescales, $t_{\rm orb}$, of thin accretion disc models as a function of emission wavelength from 1000 to 10000 Angstrom, $M_{\rm BH}$ from $10^6$ to $10^{11}$ solar masses, and Eddington ratios from 0.01 to 1. At low $M_{\rm BH}$, we find the textbook behaviour of $t_{\rm orb}\propto M_{\rm BH}^{-1/2}$ alongside $R_{\rm mean} \approx$ const, while towards higher masses the growing event horizon imposes $R_{\rm mean} \propto M_{\rm BH}$ and thus a turnover into $t_{\rm orb}\propto M_{\rm BH}$. We fit smoothly broken power laws to the numerical results and provide analytic convenience functions for $R_{\rm mean}(\lambda,M_{\rm BH},L_{3000})$ and $t_{\rm orb}(\lambda,M_{\rm BH},L_{3000})$ in terms of the observables $\lambda$, $M_{\rm BH}$, and the monochromatic luminosity $L_{3000}$. We then calculate variability structure functions for the ~2200 brightest quasars in the sky with estimates for $M_{\rm BH}$ and $L_{3000}$, using lightcurves from NASA/ATLAS orange passband spanning more than 7 years. The median luminosity of the accretion disc sample is $\log L_{\rm bol}/(\mathrm{erg\,s}^{-1})\approx 47$ and the median $\log M_{\rm BH}/M_\odot\approx 9.35$. At this high mass, the theoretical mass dependence of disc timescales levels off and turns over. The data show a weak dependence of variability on $M_{\rm BH}$ consistent with the turnover and a model where disc timescale drives variability amplitudes in the form $\log A/A_0=1/2\times\Delta t/t_{\rm orb}$, as suggested before. In the future, if the black-hole mass is known, observations of variability might be used as diagnostics of the physical luminosity in accretion discs, and therefore constrain inclination or dust extinction.

Authors: C. Wolf, S. Lai, J. -J. Tang, J. Tonry

Last Update: 2024-11-04 00:00:00

Language: English

Source URL: https://arxiv.org/abs/2411.02759

Source PDF: https://arxiv.org/pdf/2411.02759

Licence: https://creativecommons.org/licenses/by/4.0/

Changes: This summary was created with assistance from AI and may have inaccuracies. For accurate information, please refer to the original source documents linked here.

Thank you to arxiv for use of its open access interoperability.

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