Amir Siraj

Amir Siraj
Harvard University | Harvard · Department of Astronomy

About

40
Publications
1,211
Reads
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114
Citations

Publications

Publications (40)
Article
Previous works have shown that dust particles can be accelerated to marginally relativistic velocities in supernova. In this paper we consider the observational signatures of the interactions of such particles with the Earth’s atmosphere. We develop a hydrodynamic and radiative model to explore the detectability of ≳1mm sub-relativistic meteoroids....
Preprint
The upcoming commencement of the Vera C. Rubin Observatory's Legacy Survey of Space of Time (LSST) will greatly enhance the discovery rate of interstellar objects (ISOs). `Oumuamua and Borisov were the first two ISOs confirmed in the Solar system, although the first interstellar meteor may have been discovered earlier. We discuss the properties of...
Article
What is the chance we start a conversation with another civilization like our own? Our technological society produced signals that could be received by other extraterrestrial civilizations, within a sphere around us with a radius of ∼102 light years. Given that, the Copernican principle provides a lower limit on the response time that we should exp...
Preprint
If interstellar objects originate in protoplanetary disks, they can be used to calibrate the fraction of mass that such disks eject. The discoveries of interstellar objects 1I/`Oumuamua and 2I/Borisov, taken together with rogue planets statistics, allow for the calibration of mass locked in interstellar objects in size range $\sim 10^{4} - 10^{9} \...
Article
Here, we show that the detection of Borisov implies that interstellar objects outnumber Solar system objects in the Oort cloud, whereas the reverse is true near the Sun due to the stronger gravitational focusing of bound objects. This hypothesis can be tested with stellar occultation surveys of the Oort cloud. Furthermore, we demonstrate that $\sim...
Preprint
We reply to criticisms by Desch et al. (2021) regarding our Scientific Reports paper, Breakup of a long-period comet as the origin of the dinosaur extinction. The background impact rates of main-belt asteroids and long-period comets have been previously dismissed as being too low to explain the Chicxulub impact event. Our work demonstrates that a f...
Preprint
The nature of dark matter (DM) is unknown. One compelling possibility is DM being composed of primordial black holes (PBHs), given the tight limits on some types of elementary particles as DM. Here, we show that Neptune's orbital eccentricity places constraints on PBHs in the sub-solar mass window. We also derive new limits on the local abundance o...
Article
The stellar halo contains some of the oldest stars in the Milky Way galaxy and in the universe. The detections of ‘Oumuamua, CNEOS 2014-01-08, and interstellar dust serve to calibrate the production rate of interstellar objects. We study the feasibility of a search for interstellar meteors with origins in the stellar halo. We find the mean heliocen...
Preprint
The nature of dark matter (DM) is unknown. One compelling possibility is DM being composed of primordial black holes (PBHs), given the tight limits on some types of elementary particles as DM. There is only one remaining window of masses available for PBHs to constitute the entire DM density, $10^{17} - 10^{23} \mathrm{\; g}$. Here, we show that th...
Article
Full-text available
The origin of the Chicxulub impactor, which is attributed as the cause of the K/T mass extinction event, is an unsolved puzzle. The background impact rates of main-belt asteroids and long-period comets have been previously dismissed as being too low to explain the Chicxulub impact event. Here, we show that a fraction of long-period comets are tidal...
Preprint
The origin of the Chicxulub impactor, which is attributed as the cause of the K/T mass extinction event, is an unsolved puzzle. The background impact rates of main-belt asteroids and long-period comets have been previously dismissed as being too low to explain the Chicxulub impact event. Here, we show that a fraction of long-period comets are tidal...
Preprint
Recently, phosphine was discovered in the atmosphere of Venus as a potential biosignature. This raises the question: if Venusian life exists, could it be related to terrestrial life? Based on the known rate of meteoroid impacts on Earth, we show that at least $\sim 6 \times 10^5$ asteroids have grazed Earth's atmosphere without being significantly...
Preprint
There is evidence that ejecta from nearby supernovae have rained down on Earth in the past. Supernovae can accelerate pre-existing dust grains in the interstellar medium to speeds of $\sim 0.01 \mathrm{\;c}$. We investigate the survival and impact of dust grains from supernovae on the moon, finding that supernova dust grains can form detectable tra...
Article
Full-text available
Recently, a 30-cm object was discovered to graze the Earth’s atmosphere and shift into a Jupiter-crossing orbit. We use the related survey parameters to calibrate the total number of such objects. The number of objects that could have exported terrestrial microbes out of the Solar System is in the range 2 × 10 9 – 3 × 10 11 . We find that 10 7 – 10...
Article
The discovery of ‘Oumuamua and CNEOS 2014-01-08 allowed for a calibration of the impact rate of interstellar objects. We propose a new telescope in lunar orbit to study in real-time interstellar meteoroid impacts and to serve as a laboratory for hypervelocity collisions. We show that a telescope with diameter Da≳2m would be capable of detecting ≳1...
Preprint
Water plumes erupting from the `tiger stripe' features on the south pole of Enceladus are thought to connect to a global subsurface ocean. Proposed origins for the initial stress necessary to form the `tiger stripes' include a giant impact, which would require true polar wander, or tensile stresses, which would require a partial freezing of the sub...
Preprint
It is currently unknown whether solid particles larger than dust from supernova ejecta rain down on Earth at high speeds. We develop a hydrodynamic and radiative model to explore the detectability of $\gtrsim 1 \mathrm{\; mm}$ sub-relativistic meteors. We find that a large fraction of the meteor energy during its passage through the Earth's upper a...
Article
Exporting terrestrial life out of the Solar System requires a process that both embeds microbes in boulders and ejects those boulders out of the Solar System. We explore the possibility that Earthgrazing long-period comets (LPCs) and interstellar objects (ISOs) could export life from Earth by collecting microbes from the atmosphere and receiving a...
Preprint
Stellar occultations have been used to search for Kuiper Belt and Oort Cloud objects. We propose a search for interstellar objects based on the characteristic durations ($\sim 0.1 \mathrm{s}$) of their stellar occultation signals and high inclination relative to the ecliptic plane. An all-sky monitoring program of $\sim 2 \times 10^7$ stars with an...
Preprint
Recently, a 30 cm object was discovered to graze the Earth's atmosphere and shift into a Jupiter-crossing orbit. We use the related survey parameters to calibrate the total number of such objects. The number of objects that could have exported terrestrial microbes out of the Solar System is in the range $2 \times 10^{9} - 3 \times 10^{11}$. We find...
Preprint
Exporting terrestrial life out of the Solar System requires a process that both embeds microbes in boulders and ejects those boulders out of the Solar System. We explore the possibility that Earthgrazing long-period comets and interstellar objects could export life from Earth by collecting microbes from the atmosphere and receiving a gravitational...
Preprint
C/2019 Q4 (Borisov), discovered by Gennady Borisov on August 30, 2019, is tentatively an interstellar comet. We show that a kilometer-scale nucleus would provide consistency with both `Oumuamua and CNEOS-2014-01-08, resulting in a single power-law distribution with an equal amount of mass per logarithmic bin of interstellar objects.
Preprint
We propose that collisions between neutron stars and interstellar asteroids, such as `Oumuamua, could power observable radio flares in the Milky Way galaxy. We find the rate of such events at $\sim 1 \mathrm{\; Jy}$ to be $\sim 10 \mathrm{\; day^{-1}}$.
Preprint
The discovery of `Oumuamua and CNEOS 2014-01-08 allowed for a calibration of the impact rate of interstellar objects. We propose a new telescope in lunar orbit to study in real-time interstellar meteoroid impacts and to serve as a laboratory for hypervelocity collisions. We show that a telescope with diameter $D \gtrsim 2 \mathrm{\; m}$ would be ca...
Preprint
The stellar halo contains some of the oldest stars in the Milky Way galaxy and in the universe. The detections of `Oumuamua, CNEOS 2014-01-08, and interstellar dust serve to calibrate the production rate of interstellar objects. We study the feasibility of a search for interstellar meteors with origins in the stellar halo. We find the mean heliocen...
Preprint
The first interstellar object, `Oumuamua, was discovered in the Solar System by Pan-STARRS in 2017, allowing for a calibration of the impact rate of interstellar meteors of its size $\sim 100\;$m. The discovery of CNEOS 2014-01-08 allowed for a calibration of the impact rate of interstellar meteors of its size $\sim 1\;$m. Analysis of interstellar...
Preprint
The first interstellar object, `Oumuamua, was discovered in the Solar System by Pan-STARRS in 2017, allowing for a calibration of the abundance of interstellar objects of its size $\sim 100\;$ m. One would expect a much higher abundance of smaller interstellar objects, with some of them colliding with Earth frequently enough to be noticeable. Based...
Article
The first interstellar object, 'Oumuamua, was discovered in the solar system by Pan-STARRS in 2017, allowing for a calibration of the abundance of interstellar objects of its size and an estimation of the subset of objects trapped by the Jupiter-Sun system. Photographing or visiting these trapped objects would allow us to learn about the conditions...
Preprint
The first interstellar object, `Oumuamua, was discovered in the Solar System by Pan-STARRS in 2017, allowing for a calibration of the abundance of interstellar objects of its size and an estimation of the subset of objects trapped by the Jupiter-Sun system. Photographing or visiting these trapped objects would allow for learning about the condition...
Article
Full-text available
We present light curves and derive periods and amplitudes for a subset of 38 near-Earth objects (NEOs) observed at 4.5 μm with the IRAC camera on the the Spitzer Space Telescope, many of them having no previously reported rotation periods. This subset was chosen from about 1800 IRAC NEO observations as having obvious periodicity and significant amp...
Article
Full-text available
We present light curves and derive periods and amplitudes for a subset of 38 near-Earth objects (NEOs) observed at 4.5 µm with the IRAC camera on the the Spitzer Space Telescope, many of them having no previously reported rotation periods. This subset was chosen from about 1800 IRAC NEO observations as having obvious periodicity and significant amp...
Preprint
Full-text available
We present lightcurves and derive periods and amplitudes for a subset of 38 near earth objects (NEOs) observed at 4.5 microns with the IRAC camera on the the Spitzer Space Telescope, many of them having no previously reported rotation periods. This subset was chosen from about 1800 IRAC NEO observations as having obvious periodicity and significant...
Article
We present lightcurves and derive periods and amplitudes for a subset of 38 near earth objects(NEOs) observed at 4.5 microns with the IRAC camera on the the Spitzer Space Telescope, many of them having no previously reported rotation periods. This subset was chosen from about 1800 IRAC NEO observations as having obvious periodicity and significant...

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